* [PATCH] xen: Don't disable the REP emulation optimizations for regular IO
@ 2016-03-10 10:07 Razvan Cojocaru
2016-03-10 10:22 ` Jan Beulich
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: Razvan Cojocaru @ 2016-03-10 10:07 UTC (permalink / raw)
To: xen-devel; +Cc: andrew.cooper3, keir, Razvan Cojocaru, jbeulich
Currently REP emulations optimizations remain disabled even if
the emulation does not happen as a result of a vm_event reply
requestion emulation (i.e. even for regular IO). This patch takes
emulate_each_rep into account only if emulation has been requested
by a vm_event-capable application, and is a noticeable speed
optimization for monitored guests.
Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
---
xen/arch/x86/hvm/emulate.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)
diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index 082aa30..ddc8007 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -498,6 +498,7 @@ static int hvmemul_virtual_to_linear(
{
struct segment_register *reg;
int okay;
+ unsigned long max_reps = 4096;
if ( seg == x86_seg_none )
{
@@ -506,16 +507,21 @@ static int hvmemul_virtual_to_linear(
}
/*
+ * If introspection has been enabled for this domain, and we're emulating
+ * becase a vm_reply asked us to (i.e. not doing regular IO) reps should
+ * be at most 1, since optimization might otherwise cause a single
+ * vm_event being triggered for repeated writes to a whole page.
+ */
+ if ( unlikely(current->domain->arch.mem_access_emulate_each_rep) &&
+ current->arch.vm_event->emulate_flags != 0 )
+ max_reps = 1;
+
+ /*
* Clip repetitions to avoid overflow when multiplying by @bytes_per_rep.
* The chosen maximum is very conservative but it's what we use in
* hvmemul_linear_to_phys() so there is no point in using a larger value.
- * If introspection has been enabled for this domain, *reps should be
- * at most 1, since optimization might otherwise cause a single vm_event
- * being triggered for repeated writes to a whole page.
*/
- *reps = min_t(unsigned long, *reps,
- unlikely(current->domain->arch.mem_access_emulate_each_rep)
- ? 1 : 4096);
+ *reps = min_t(unsigned long, *reps, max_reps);
reg = hvmemul_get_seg_reg(seg, hvmemul_ctxt);
--
1.9.1
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^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] xen: Don't disable the REP emulation optimizations for regular IO
2016-03-10 10:07 [PATCH] xen: Don't disable the REP emulation optimizations for regular IO Razvan Cojocaru
@ 2016-03-10 10:22 ` Jan Beulich
2016-03-10 11:22 ` Andrew Cooper
2016-03-10 14:28 ` Tamas K Lengyel
2 siblings, 0 replies; 4+ messages in thread
From: Jan Beulich @ 2016-03-10 10:22 UTC (permalink / raw)
To: Razvan Cojocaru; +Cc: andrew.cooper3, tamas, keir, xen-devel
>>> On 10.03.16 at 11:07, <rcojocaru@bitdefender.com> wrote:
> Currently REP emulations optimizations remain disabled even if
> the emulation does not happen as a result of a vm_event reply
> requestion emulation (i.e. even for regular IO). This patch takes
> emulate_each_rep into account only if emulation has been requested
> by a vm_event-capable application, and is a noticeable speed
> optimization for monitored guests.
>
> Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Looks reasonable, but this being an event specific change I'm
making my ack to this dependent on Tamas'es consent.
Jan
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -498,6 +498,7 @@ static int hvmemul_virtual_to_linear(
> {
> struct segment_register *reg;
> int okay;
> + unsigned long max_reps = 4096;
>
> if ( seg == x86_seg_none )
> {
> @@ -506,16 +507,21 @@ static int hvmemul_virtual_to_linear(
> }
>
> /*
> + * If introspection has been enabled for this domain, and we're emulating
> + * becase a vm_reply asked us to (i.e. not doing regular IO) reps should
> + * be at most 1, since optimization might otherwise cause a single
> + * vm_event being triggered for repeated writes to a whole page.
> + */
> + if ( unlikely(current->domain->arch.mem_access_emulate_each_rep) &&
> + current->arch.vm_event->emulate_flags != 0 )
> + max_reps = 1;
> +
> + /*
> * Clip repetitions to avoid overflow when multiplying by @bytes_per_rep.
> * The chosen maximum is very conservative but it's what we use in
> * hvmemul_linear_to_phys() so there is no point in using a larger value.
> - * If introspection has been enabled for this domain, *reps should be
> - * at most 1, since optimization might otherwise cause a single vm_event
> - * being triggered for repeated writes to a whole page.
> */
> - *reps = min_t(unsigned long, *reps,
> - unlikely(current->domain->arch.mem_access_emulate_each_rep)
> - ? 1 : 4096);
> + *reps = min_t(unsigned long, *reps, max_reps);
>
> reg = hvmemul_get_seg_reg(seg, hvmemul_ctxt);
>
> --
> 1.9.1
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] xen: Don't disable the REP emulation optimizations for regular IO
2016-03-10 10:07 [PATCH] xen: Don't disable the REP emulation optimizations for regular IO Razvan Cojocaru
2016-03-10 10:22 ` Jan Beulich
@ 2016-03-10 11:22 ` Andrew Cooper
2016-03-10 14:28 ` Tamas K Lengyel
2 siblings, 0 replies; 4+ messages in thread
From: Andrew Cooper @ 2016-03-10 11:22 UTC (permalink / raw)
To: Razvan Cojocaru, xen-devel; +Cc: keir, jbeulich
On 10/03/16 10:07, Razvan Cojocaru wrote:
> Currently REP emulations optimizations remain disabled even if
> the emulation does not happen as a result of a vm_event reply
> requestion emulation (i.e. even for regular IO). This patch takes
> emulate_each_rep into account only if emulation has been requested
> by a vm_event-capable application, and is a noticeable speed
> optimization for monitored guests.
>
> Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] xen: Don't disable the REP emulation optimizations for regular IO
2016-03-10 10:07 [PATCH] xen: Don't disable the REP emulation optimizations for regular IO Razvan Cojocaru
2016-03-10 10:22 ` Jan Beulich
2016-03-10 11:22 ` Andrew Cooper
@ 2016-03-10 14:28 ` Tamas K Lengyel
2 siblings, 0 replies; 4+ messages in thread
From: Tamas K Lengyel @ 2016-03-10 14:28 UTC (permalink / raw)
To: Razvan Cojocaru; +Cc: andrew.cooper3, Keir Fraser, jbeulich, xen-devel
[-- Attachment #1.1: Type: text/plain, Size: 2499 bytes --]
On Mar 10, 2016 11:09, "Razvan Cojocaru" <rcojocaru@bitdefender.com> wrote:
>
> Currently REP emulations optimizations remain disabled even if
> the emulation does not happen as a result of a vm_event reply
> requestion emulation (i.e. even for regular IO). This patch takes
> emulate_each_rep into account only if emulation has been requested
> by a vm_event-capable application, and is a noticeable speed
> optimization for monitored guests.
>
> Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Reviewed-by: Tamas K Lengyel <tamas@tklengyel.com>
> ---
> xen/arch/x86/hvm/emulate.c | 18 ++++++++++++------
> 1 file changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
> index 082aa30..ddc8007 100644
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -498,6 +498,7 @@ static int hvmemul_virtual_to_linear(
> {
> struct segment_register *reg;
> int okay;
> + unsigned long max_reps = 4096;
>
> if ( seg == x86_seg_none )
> {
> @@ -506,16 +507,21 @@ static int hvmemul_virtual_to_linear(
> }
>
> /*
> + * If introspection has been enabled for this domain, and we're
emulating
> + * becase a vm_reply asked us to (i.e. not doing regular IO) reps
should
> + * be at most 1, since optimization might otherwise cause a single
> + * vm_event being triggered for repeated writes to a whole page.
> + */
> + if ( unlikely(current->domain->arch.mem_access_emulate_each_rep) &&
> + current->arch.vm_event->emulate_flags != 0 )
> + max_reps = 1;
> +
> + /*
> * Clip repetitions to avoid overflow when multiplying by
@bytes_per_rep.
> * The chosen maximum is very conservative but it's what we use in
> * hvmemul_linear_to_phys() so there is no point in using a larger
value.
> - * If introspection has been enabled for this domain, *reps should be
> - * at most 1, since optimization might otherwise cause a single
vm_event
> - * being triggered for repeated writes to a whole page.
> */
> - *reps = min_t(unsigned long, *reps,
> -
unlikely(current->domain->arch.mem_access_emulate_each_rep)
> - ? 1 : 4096);
> + *reps = min_t(unsigned long, *reps, max_reps);
>
> reg = hvmemul_get_seg_reg(seg, hvmemul_ctxt);
>
> --
> 1.9.1
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
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2016-03-10 10:07 [PATCH] xen: Don't disable the REP emulation optimizations for regular IO Razvan Cojocaru
2016-03-10 10:22 ` Jan Beulich
2016-03-10 11:22 ` Andrew Cooper
2016-03-10 14:28 ` Tamas K Lengyel
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