[Qemu-devel] [PATCH v3 0/3] throttle: improve command-line parameter documentation

[Qemu-devel] [PATCH v3 0/3] throttle: improve command-line parameter documentation

[Stefan Hajnoczi]

v3:
 * Added Patch 2 to fix invalid test parameters
 * Switched to nicer max < avg check [Berto]
v2:
 * Fixed s/bps/iops/ copy-paste error in Patch 1 [Berto]
 * Rephrased warning about guest hangs and errors [Berto]
 * Added Patch 2 to hide the internal .max value from the monitor

Patch 1 fleshes out the documentation for I/O throttling command-line
parameters.

Patch 2 hides an internal value that was being exposed to users via the
monitor and caused confusion.

I ended up not adding QMP-style throttling.* names to the command-line
documentation because the names are very long and unlikely to be used.  I
couldn't see a nice way of adding them while still keeping the documentation
readable.

Stefan Hajnoczi (3):
  qemu-options: explain disk I/O throttling options
  throttle: do not use invalid config in test
  throttle: make throttle_config(throttle_get_config()) symmetric

 tests/test-throttle.c |  8 ++++----
 util/throttle.c       | 14 ++++++++++++++
 qemu-options.hx       | 24 ++++++++++++++++++++++++
 3 files changed, 42 insertions(+), 4 deletions(-)

-- 
2.9.3

[Qemu-devel] [PATCH v3 1/3] qemu-options: explain disk I/O throttling options

[Stefan Hajnoczi]

The disk I/O throttling options have been listed for a long time but
never explained on the QEMU man page.

Suggested-by: Nini Gu <ngu@redhat.com>
Cc: Alberto Garcia <berto@igalia.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 qemu-options.hx | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/qemu-options.hx b/qemu-options.hx
index c85f77d..bbd1bd9 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -607,6 +607,30 @@ file sectors into the image file.
 conversion of plain zero writes by the OS to driver specific optimized
 zero write commands. You may even choose "unmap" if @var{discard} is set
 to "unmap" to allow a zero write to be converted to an UNMAP operation.
+@item bps=@var{b},bps_rd=@var{r},bps_wr=@var{w}
+Specify bandwidth throttling limits in bytes per second, either for all request
+types or for reads or writes only.  Small values can lead to timeouts or hangs
+inside the guest.  A safe minimum for disks is 2 MB/s.
+@item bps_max=@var{bm},bps_rd_max=@var{rm},bps_wr_max=@var{wm}
+Specify bursts in bytes per second, either for all request types or for reads
+or writes only.  Bursts allow the guest I/O to spike above the limit
+temporarily.
+@item iops=@var{i},iops_rd=@var{r},iops_wr=@var{w}
+Specify request rate limits in requests per second, either for all request
+types or for reads or writes only.
+@item iops_max=@var{bm},iops_rd_max=@var{rm},iops_wr_max=@var{wm}
+Specify bursts in requests per second, either for all request types or for reads
+or writes only.  Bursts allow the guest I/O to spike above the limit
+temporarily.
+@item iops_size=@var{is}
+Let every @var{is} bytes of a request count as a new request for iops
+throttling purposes.  Use this option to prevent guests from circumventing iops
+limits by sending fewer but larger requests.
+@item group=@var{g}
+Join a throttling quota group with given name @var{g}.  All drives that are
+members of the same group are accounted for together.  Use this option to
+prevent guests from circumventing throttling limits by using many small disks
+instead of a single larger disk.
 @end table
 
 By default, the @option{cache=writeback} mode is used. It will report data
-- 
2.9.3

Re: [Qemu-devel] [PATCH v3 1/3] qemu-options: explain disk I/O throttling options

[Alberto Garcia]

On Wed 01 Mar 2017 12:50:24 PM CET, Stefan Hajnoczi wrote:
> The disk I/O throttling options have been listed for a long time but
> never explained on the QEMU man page.
>
> Suggested-by: Nini Gu <ngu@redhat.com>
> Cc: Alberto Garcia <berto@igalia.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Alberto Garcia <berto@igalia.com>

Berto

Re: [Qemu-devel] [PATCH v3 1/3] qemu-options: explain disk I/O throttling options

[Greg Kurz]

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On Wed,  1 Mar 2017 11:50:24 +0000
Stefan Hajnoczi <stefanha@redhat.com> wrote:

> The disk I/O throttling options have been listed for a long time but
> never explained on the QEMU man page.
> 
> Suggested-by: Nini Gu <ngu@redhat.com>
> Cc: Alberto Garcia <berto@igalia.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---

Reviewed-by: Greg Kurz <groug@kaod.org>

>  qemu-options.hx | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/qemu-options.hx b/qemu-options.hx
> index c85f77d..bbd1bd9 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -607,6 +607,30 @@ file sectors into the image file.
>  conversion of plain zero writes by the OS to driver specific optimized
>  zero write commands. You may even choose "unmap" if @var{discard} is set
>  to "unmap" to allow a zero write to be converted to an UNMAP operation.
> +@item bps=@var{b},bps_rd=@var{r},bps_wr=@var{w}
> +Specify bandwidth throttling limits in bytes per second, either for all request
> +types or for reads or writes only.  Small values can lead to timeouts or hangs
> +inside the guest.  A safe minimum for disks is 2 MB/s.
> +@item bps_max=@var{bm},bps_rd_max=@var{rm},bps_wr_max=@var{wm}
> +Specify bursts in bytes per second, either for all request types or for reads
> +or writes only.  Bursts allow the guest I/O to spike above the limit
> +temporarily.
> +@item iops=@var{i},iops_rd=@var{r},iops_wr=@var{w}
> +Specify request rate limits in requests per second, either for all request
> +types or for reads or writes only.
> +@item iops_max=@var{bm},iops_rd_max=@var{rm},iops_wr_max=@var{wm}
> +Specify bursts in requests per second, either for all request types or for reads
> +or writes only.  Bursts allow the guest I/O to spike above the limit
> +temporarily.
> +@item iops_size=@var{is}
> +Let every @var{is} bytes of a request count as a new request for iops
> +throttling purposes.  Use this option to prevent guests from circumventing iops
> +limits by sending fewer but larger requests.
> +@item group=@var{g}
> +Join a throttling quota group with given name @var{g}.  All drives that are
> +members of the same group are accounted for together.  Use this option to
> +prevent guests from circumventing throttling limits by using many small disks
> +instead of a single larger disk.
>  @end table
>  
>  By default, the @option{cache=writeback} mode is used. It will report data


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[Qemu-devel] [PATCH v3 2/3] throttle: do not use invalid config in test

[Stefan Hajnoczi]

The (burst) max parameter cannot be smaller than the avg parameter.
There is a test case that uses avg = 56, max = 1 and gets away with it
because no input validation is performed by the test case.

This patch switches to valid test input parameters.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 tests/test-throttle.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tests/test-throttle.c b/tests/test-throttle.c
index 363b59a..8531809 100644
--- a/tests/test-throttle.c
+++ b/tests/test-throttle.c
@@ -205,8 +205,8 @@ static void test_config_functions(void)
     orig_cfg.buckets[THROTTLE_OPS_READ].avg  = 69;
     orig_cfg.buckets[THROTTLE_OPS_WRITE].avg = 23;
 
-    orig_cfg.buckets[THROTTLE_BPS_TOTAL].max = 0; /* should be corrected */
-    orig_cfg.buckets[THROTTLE_BPS_READ].max  = 1; /* should not be corrected */
+    orig_cfg.buckets[THROTTLE_BPS_TOTAL].max = 0;  /* should be corrected */
+    orig_cfg.buckets[THROTTLE_BPS_READ].max  = 56; /* should not be corrected */
     orig_cfg.buckets[THROTTLE_BPS_WRITE].max = 120;
 
     orig_cfg.buckets[THROTTLE_OPS_TOTAL].max = 150;
@@ -246,8 +246,8 @@ static void test_config_functions(void)
     g_assert(final_cfg.buckets[THROTTLE_OPS_READ].avg  == 69);
     g_assert(final_cfg.buckets[THROTTLE_OPS_WRITE].avg == 23);
 
-    g_assert(final_cfg.buckets[THROTTLE_BPS_TOTAL].max == 15.3);/* fixed */
-    g_assert(final_cfg.buckets[THROTTLE_BPS_READ].max  == 1);   /* not fixed */
+    g_assert(final_cfg.buckets[THROTTLE_BPS_TOTAL].max == 15.3); /* fixed */
+    g_assert(final_cfg.buckets[THROTTLE_BPS_READ].max  == 56);   /* not fixed */
     g_assert(final_cfg.buckets[THROTTLE_BPS_WRITE].max == 120);
 
     g_assert(final_cfg.buckets[THROTTLE_OPS_TOTAL].max == 150);
-- 
2.9.3

Re: [Qemu-devel] [PATCH v3 2/3] throttle: do not use invalid config in test

[Alberto Garcia]

On Wed 01 Mar 2017 12:50:25 PM CET, Stefan Hajnoczi wrote:
> The (burst) max parameter cannot be smaller than the avg parameter.
> There is a test case that uses avg = 56, max = 1 and gets away with it
> because no input validation is performed by the test case.
>
> This patch switches to valid test input parameters.
>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Alberto Garcia <berto@igalia.com>

Berto

[Qemu-devel] [PATCH v3 3/3] throttle: make throttle_config(throttle_get_config()) symmetric

[Stefan Hajnoczi]

Throttling has a weird property that throttle_get_config() does not
always return the same throttling settings that were given with
throttle_config().  In other words, the set and get functions aren't
symmetric.

If .max is 0 then the throttling code assigns a default value of .avg /
10 in throttle_config().  This is an implementation detail of the
throttling algorithm.  When throttle_get_config() is called the .max
value returned should still be 0.

Users are exposed to this quirk via "info block" or "query-block"
monitor commands.  This has caused confusion because it looks like a bug
when an unexpected value is reported.

This patch hides the .max value adjustment in throttle_get_config() and
updates test-throttle.c appropriately.

Reported-by: Nini Gu <ngu@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 tests/test-throttle.c |  8 ++++----
 util/throttle.c       | 14 ++++++++++++++
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/tests/test-throttle.c b/tests/test-throttle.c
index 8531809..2a8bf64 100644
--- a/tests/test-throttle.c
+++ b/tests/test-throttle.c
@@ -205,8 +205,8 @@ static void test_config_functions(void)
     orig_cfg.buckets[THROTTLE_OPS_READ].avg  = 69;
     orig_cfg.buckets[THROTTLE_OPS_WRITE].avg = 23;
 
-    orig_cfg.buckets[THROTTLE_BPS_TOTAL].max = 0;  /* should be corrected */
-    orig_cfg.buckets[THROTTLE_BPS_READ].max  = 56; /* should not be corrected */
+    orig_cfg.buckets[THROTTLE_BPS_TOTAL].max = 0;
+    orig_cfg.buckets[THROTTLE_BPS_READ].max  = 56;
     orig_cfg.buckets[THROTTLE_BPS_WRITE].max = 120;
 
     orig_cfg.buckets[THROTTLE_OPS_TOTAL].max = 150;
@@ -246,8 +246,8 @@ static void test_config_functions(void)
     g_assert(final_cfg.buckets[THROTTLE_OPS_READ].avg  == 69);
     g_assert(final_cfg.buckets[THROTTLE_OPS_WRITE].avg == 23);
 
-    g_assert(final_cfg.buckets[THROTTLE_BPS_TOTAL].max == 15.3); /* fixed */
-    g_assert(final_cfg.buckets[THROTTLE_BPS_READ].max  == 56);   /* not fixed */
+    g_assert(final_cfg.buckets[THROTTLE_BPS_TOTAL].max == 0);
+    g_assert(final_cfg.buckets[THROTTLE_BPS_READ].max  == 56);
     g_assert(final_cfg.buckets[THROTTLE_BPS_WRITE].max == 120);
 
     g_assert(final_cfg.buckets[THROTTLE_OPS_TOTAL].max == 150);
diff --git a/util/throttle.c b/util/throttle.c
index 3817d9b..3570ed2 100644
--- a/util/throttle.c
+++ b/util/throttle.c
@@ -380,6 +380,14 @@ static void throttle_fix_bucket(LeakyBucket *bkt)
     }
 }
 
+/* undo internal bucket parameter changes (see throttle_fix_bucket()) */
+static void throttle_unfix_bucket(LeakyBucket *bkt)
+{
+    if (bkt->max < bkt->avg) {
+        bkt->max = 0;
+    }
+}
+
 /* take care of canceling a timer */
 static void throttle_cancel_timer(QEMUTimer *timer)
 {
@@ -420,7 +428,13 @@ void throttle_config(ThrottleState *ts,
  */
 void throttle_get_config(ThrottleState *ts, ThrottleConfig *cfg)
 {
+    int i;
+
     *cfg = ts->cfg;
+
+    for (i = 0; i < BUCKETS_COUNT; i++) {
+        throttle_unfix_bucket(&cfg->buckets[i]);
+    }
 }
 
 
-- 
2.9.3

Re: [Qemu-devel] [PATCH v3 3/3] throttle: make throttle_config(throttle_get_config()) symmetric

[Alberto Garcia]

On Wed 01 Mar 2017 12:50:26 PM CET, Stefan Hajnoczi wrote:
> Throttling has a weird property that throttle_get_config() does not
> always return the same throttling settings that were given with
> throttle_config().  In other words, the set and get functions aren't
> symmetric.
>
> If .max is 0 then the throttling code assigns a default value of .avg /
> 10 in throttle_config().  This is an implementation detail of the
> throttling algorithm.  When throttle_get_config() is called the .max
> value returned should still be 0.
>
> Users are exposed to this quirk via "info block" or "query-block"
> monitor commands.  This has caused confusion because it looks like a bug
> when an unexpected value is reported.
>
> This patch hides the .max value adjustment in throttle_get_config() and
> updates test-throttle.c appropriately.
>
> Reported-by: Nini Gu <ngu@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Alberto Garcia <berto@igalia.com>

Berto

Re: [Qemu-devel] [PATCH v3 0/3] throttle: improve command-line parameter documentation

[Greg Kurz]

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On Wed,  1 Mar 2017 11:50:23 +0000
Stefan Hajnoczi <stefanha@redhat.com> wrote:

> v3:
>  * Added Patch 2 to fix invalid test parameters
>  * Switched to nicer max < avg check [Berto]
> v2:
>  * Fixed s/bps/iops/ copy-paste error in Patch 1 [Berto]
>  * Rephrased warning about guest hangs and errors [Berto]
>  * Added Patch 2 to hide the internal .max value from the monitor
> 
> Patch 1 fleshes out the documentation for I/O throttling command-line
> parameters.
> 
> Patch 2 hides an internal value that was being exposed to users via the
> monitor and caused confusion.
> 
> I ended up not adding QMP-style throttling.* names to the command-line
> documentation because the names are very long and unlikely to be used.  I
> couldn't see a nice way of adding them while still keeping the documentation
> readable.
> 

I only see this series now and it's a bit unfortunate... throttling options
are now also available for fsdev. Only QMP-style names were added though,
and they appear in the documentation. I agree the names are long, and the
result isn't pretty on 80 columns, but it is readable still.

I don't really want to add code, just to have shorter names and a prettier
output. But it would be a good thing for fsdev to benefit from this new
documentation... any suggestion how to do that ?

> Stefan Hajnoczi (3):
>   qemu-options: explain disk I/O throttling options
>   throttle: do not use invalid config in test
>   throttle: make throttle_config(throttle_get_config()) symmetric
> 
>  tests/test-throttle.c |  8 ++++----
>  util/throttle.c       | 14 ++++++++++++++
>  qemu-options.hx       | 24 ++++++++++++++++++++++++
>  3 files changed, 42 insertions(+), 4 deletions(-)
> 


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Re: [Qemu-devel] [Qemu-block] [PATCH v3 0/3] throttle: improve command-line parameter documentation

[Stefan Hajnoczi]

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On Wed, Mar 01, 2017 at 10:27:48PM +0100, Greg Kurz wrote:
> On Wed,  1 Mar 2017 11:50:23 +0000
> Stefan Hajnoczi <stefanha@redhat.com> wrote:
> 
> > v3:
> >  * Added Patch 2 to fix invalid test parameters
> >  * Switched to nicer max < avg check [Berto]
> > v2:
> >  * Fixed s/bps/iops/ copy-paste error in Patch 1 [Berto]
> >  * Rephrased warning about guest hangs and errors [Berto]
> >  * Added Patch 2 to hide the internal .max value from the monitor
> > 
> > Patch 1 fleshes out the documentation for I/O throttling command-line
> > parameters.
> > 
> > Patch 2 hides an internal value that was being exposed to users via the
> > monitor and caused confusion.
> > 
> > I ended up not adding QMP-style throttling.* names to the command-line
> > documentation because the names are very long and unlikely to be used.  I
> > couldn't see a nice way of adding them while still keeping the documentation
> > readable.
> > 
> 
> I only see this series now and it's a bit unfortunate... throttling options
> are now also available for fsdev. Only QMP-style names were added though,
> and they appear in the documentation. I agree the names are long, and the
> result isn't pretty on 80 columns, but it is readable still.
> 
> I don't really want to add code, just to have shorter names and a prettier
> output. But it would be a good thing for fsdev to benefit from this new
> documentation... any suggestion how to do that ?

I think another patch series would be good to:
1. Document QMP-style names for -drive
2. Reference throttling parameter documention in a common place for both
   -fsdev and -drive.

I'll do that.  This is QEMU 2.10 material anyway (it has missed the
freeze deadline), so there's no time pressure.

Stefan

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Re: [Qemu-devel] [Qemu-block] [PATCH v3 0/3] throttle: improve command-line parameter documentation

[Greg Kurz]

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On Fri, 3 Mar 2017 10:11:09 +0800
Stefan Hajnoczi <stefanha@gmail.com> wrote:

> On Wed, Mar 01, 2017 at 10:27:48PM +0100, Greg Kurz wrote:
> > On Wed,  1 Mar 2017 11:50:23 +0000
> > Stefan Hajnoczi <stefanha@redhat.com> wrote:
> >   
> > > v3:
> > >  * Added Patch 2 to fix invalid test parameters
> > >  * Switched to nicer max < avg check [Berto]
> > > v2:
> > >  * Fixed s/bps/iops/ copy-paste error in Patch 1 [Berto]
> > >  * Rephrased warning about guest hangs and errors [Berto]
> > >  * Added Patch 2 to hide the internal .max value from the monitor
> > > 
> > > Patch 1 fleshes out the documentation for I/O throttling command-line
> > > parameters.
> > > 
> > > Patch 2 hides an internal value that was being exposed to users via the
> > > monitor and caused confusion.
> > > 
> > > I ended up not adding QMP-style throttling.* names to the command-line
> > > documentation because the names are very long and unlikely to be used.  I
> > > couldn't see a nice way of adding them while still keeping the documentation
> > > readable.
> > >   
> > 
> > I only see this series now and it's a bit unfortunate... throttling options
> > are now also available for fsdev. Only QMP-style names were added though,
> > and they appear in the documentation. I agree the names are long, and the
> > result isn't pretty on 80 columns, but it is readable still.
> > 
> > I don't really want to add code, just to have shorter names and a prettier
> > output. But it would be a good thing for fsdev to benefit from this new
> > documentation... any suggestion how to do that ?  
> 
> I think another patch series would be good to:
> 1. Document QMP-style names for -drive
> 2. Reference throttling parameter documention in a common place for both
>    -fsdev and -drive.
> 
> I'll do that.  This is QEMU 2.10 material anyway (it has missed the
> freeze deadline), so there's no time pressure.
> 
> Stefan

Sure. Please Cc me when you do that.

Thanks.

--
Greg

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Re: [Qemu-devel] [Qemu-block] [PATCH v3 0/3] throttle: improve command-line parameter documentation

[Stefan Hajnoczi]

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On Wed, Mar 01, 2017 at 11:50:23AM +0000, Stefan Hajnoczi wrote:
> v3:
>  * Added Patch 2 to fix invalid test parameters
>  * Switched to nicer max < avg check [Berto]
> v2:
>  * Fixed s/bps/iops/ copy-paste error in Patch 1 [Berto]
>  * Rephrased warning about guest hangs and errors [Berto]
>  * Added Patch 2 to hide the internal .max value from the monitor
> 
> Patch 1 fleshes out the documentation for I/O throttling command-line
> parameters.
> 
> Patch 2 hides an internal value that was being exposed to users via the
> monitor and caused confusion.
> 
> I ended up not adding QMP-style throttling.* names to the command-line
> documentation because the names are very long and unlikely to be used.  I
> couldn't see a nice way of adding them while still keeping the documentation
> readable.
> 
> Stefan Hajnoczi (3):
>   qemu-options: explain disk I/O throttling options
>   throttle: do not use invalid config in test
>   throttle: make throttle_config(throttle_get_config()) symmetric
> 
>  tests/test-throttle.c |  8 ++++----
>  util/throttle.c       | 14 ++++++++++++++
>  qemu-options.hx       | 24 ++++++++++++++++++++++++
>  3 files changed, 42 insertions(+), 4 deletions(-)
> 
> -- 
> 2.9.3
> 
> 

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan

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