* BFQ cgroup weights range @ 2021-08-24 10:56 Michal Koutný 2021-08-24 12:51 ` Paolo Valente 0 siblings, 1 reply; 6+ messages in thread From: Michal Koutný @ 2021-08-24 10:56 UTC (permalink / raw) To: Paolo Valente, Jens Axboe; +Cc: linux-block, Jan Kara, Michal Koutný Hello. The default weight for proportional IO control associated with a cgroup is 100 [1]. The minimum allowed weight is 1 [2] and the maximum weight 1000 [3]. This is a bit inconsistent with general cgroup weight semantic where def/min == max/def (i.e. symmetric adjustments to both sides) [4]. 1) Is there a reason why the maximum allowed weight is (only) 1000? (E.g. it won't be possible to ensure 10^4 ratio of proportional control but 10^3 is achievable.) 2) Is the default value 100 special or absolute in a sense? (I suspect it is, the unchangeable weight of root cgroup members. Therefore two siblings with equal ratios 10:100 and 100:1000 would behave same only when there's no interfering IO from the root.) Thanks, Michal [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/block/bfq-cgroup.c?h=v5.14-rc7#n513 [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/block/bfq-iosched.h?h=v5.14-rc7#n18 [3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/block/bfq-iosched.h?h=v5.14-rc7#n19 [4] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/admin-guide/cgroup-v2.rst?h=v5.14-rc7#n602 ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: BFQ cgroup weights range 2021-08-24 10:56 BFQ cgroup weights range Michal Koutný @ 2021-08-24 12:51 ` Paolo Valente 2021-08-26 13:12 ` Michal Koutný 0 siblings, 1 reply; 6+ messages in thread From: Paolo Valente @ 2021-08-24 12:51 UTC (permalink / raw) To: Michal Koutný; +Cc: Jens Axboe, linux-block, Jan Kara > Il giorno 24 ago 2021, alle ore 12:56, Michal Koutný <mkoutny@suse.com> ha scritto: > > Hello. > > The default weight for proportional IO control associated with a cgroup > is 100 [1]. The minimum allowed weight is 1 [2] and the maximum weight > 1000 [3]. This is a bit inconsistent with general cgroup weight > semantic where def/min == max/def (i.e. symmetric adjustments to both > sides) [4]. > > 1) Is there a reason why the maximum allowed weight is (only) 1000? > (E.g. it won't be possible to ensure 10^4 ratio of proportional > control but 10^3 is achievable.) > 2) Is the default value 100 special or absolute in a sense? (I suspect > it is, the unchangeable weight of root cgroup members. Therefore two > siblings with equal ratios 10:100 and 100:1000 would behave same only > when there's no interfering IO from the root.) > Hi, BFQ inherited these constants when we forked it from CFQ. I'm ok with increasing max weight to 10000. I only wonder whether this would break some configuration, as the currently maximum weight would not be the maximum weight any longer. \x14 Thanks, Paolo > Thanks, > Michal > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/block/bfq-cgroup.c?h=v5.14-rc7#n513 > [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/block/bfq-iosched.h?h=v5.14-rc7#n18 > [3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/block/bfq-iosched.h?h=v5.14-rc7#n19 > [4] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/admin-guide/cgroup-v2.rst?h=v5.14-rc7#n602 ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: BFQ cgroup weights range 2021-08-24 12:51 ` Paolo Valente @ 2021-08-26 13:12 ` Michal Koutný 2021-08-26 17:25 ` Tejun Heo 0 siblings, 1 reply; 6+ messages in thread From: Michal Koutný @ 2021-08-26 13:12 UTC (permalink / raw) To: Paolo Valente; +Cc: Jens Axboe, linux-block, Jan Kara, cgroups On Tue, Aug 24, 2021 at 02:51:47PM +0200, Paolo Valente <paolo.valente@linaro.org> wrote: > BFQ inherited these constants when we forked it from CFQ. I'm ok with > increasing max weight to 10000. I only wonder whether this would > break some configuration, as the currently maximum weight would not be > the maximum weight any longer. Thanks for the reply. Let me form the idea as a patch (and commit message) and discuss based on that if needed (+ccrosspost into cgroups ML). -- >8 -- From: Michal Koutný <mkoutny@suse.com> Subject: [PATCH] block, bfq: Accept symmetric weight adjustments The allowed range for BFQ weights is currently 1..1000 with 100 being the default. There is no apparent reason to not accept weight adjustments of same ratio on both sides of the default. This change makes the attribute domain consistent with other cgroup (v2) knobs with the weight semantics. This extension of the range does not restrict existing configurations (quite the opposite). This may affect setups where weights >1000 were attempted to be set but failed with the default 100. Such cgroups would attain their intended weight now. This is a changed behavior but it rectifies the situation (similar intention to the commit 69d7fde5909b ("blkcg: use CGROUP_WEIGHT_* scale for io.weight on the unified hierarchy") for CFQ formerly (and v2 only)). Additionally, the changed range does not imply all IO workloads can be really controlled to achieve the widest possible ratio 1:10^4. Signed-off-by: Michal Koutný <mkoutny@suse.com> --- Documentation/admin-guide/cgroup-v1/blkio-controller.rst | 2 +- Documentation/block/bfq-iosched.rst | 2 +- block/bfq-iosched.h | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-) diff --git a/Documentation/admin-guide/cgroup-v1/blkio-controller.rst b/Documentation/admin-guide/cgroup-v1/blkio-controller.rst index 16253eda192e..48559541c9d8 100644 --- a/Documentation/admin-guide/cgroup-v1/blkio-controller.rst +++ b/Documentation/admin-guide/cgroup-v1/blkio-controller.rst @@ -102,7 +102,7 @@ Proportional weight policy files on all the devices until and unless overridden by per device rule (see `blkio.bfq.weight_device` below). - Currently allowed range of weights is from 1 to 1000. For more details, + Currently allowed range of weights is from 1 to 10000. For more details, see Documentation/block/bfq-iosched.rst. blkio.bfq.weight_device diff --git a/Documentation/block/bfq-iosched.rst b/Documentation/block/bfq-iosched.rst index df3a8a47f58c..88b5251734ce 100644 --- a/Documentation/block/bfq-iosched.rst +++ b/Documentation/block/bfq-iosched.rst @@ -560,7 +560,7 @@ For each group, the following parameters can be set: weight This specifies the default weight for the cgroup inside its parent. - Available values: 1..1000 (default: 100). + Available values: 1..10000 (default: 100). For cgroup v1, it is set by writing the value to `blkio.bfq.weight`. diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h index 99c2a3cb081e..786b7f926dd2 100644 --- a/block/bfq-iosched.h +++ b/block/bfq-iosched.h @@ -16,7 +16,7 @@ #define BFQ_CL_IDLE_TIMEOUT (HZ/5) #define BFQ_MIN_WEIGHT 1 -#define BFQ_MAX_WEIGHT 1000 +#define BFQ_MAX_WEIGHT 10000 #define BFQ_WEIGHT_CONVERSION_COEFF 10 #define BFQ_DEFAULT_QUEUE_IOPRIO 4 -- 2.32.0 ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: BFQ cgroup weights range 2021-08-26 13:12 ` Michal Koutný @ 2021-08-26 17:25 ` Tejun Heo 2021-08-27 8:33 ` Paolo Valente 0 siblings, 1 reply; 6+ messages in thread From: Tejun Heo @ 2021-08-26 17:25 UTC (permalink / raw) To: Michal Koutný Cc: Paolo Valente, Jens Axboe, linux-block, Jan Kara, cgroups On Thu, Aug 26, 2021 at 03:12:12PM +0200, Michal Koutný wrote: > On Tue, Aug 24, 2021 at 02:51:47PM +0200, Paolo Valente <paolo.valente@linaro.org> wrote: > > BFQ inherited these constants when we forked it from CFQ. I'm ok with > > increasing max weight to 10000. I only wonder whether this would > > break some configuration, as the currently maximum weight would not be > > the maximum weight any longer. > > Thanks for the reply. Let me form the idea as a patch (and commit > message) and discuss based on that if needed (+ccrosspost into cgroups > ML). > > -- >8 -- > From: Michal Koutný <mkoutny@suse.com> > Subject: [PATCH] block, bfq: Accept symmetric weight adjustments > > The allowed range for BFQ weights is currently 1..1000 with 100 being > the default. There is no apparent reason to not accept weight > adjustments of same ratio on both sides of the default. This change > makes the attribute domain consistent with other cgroup (v2) knobs with > the weight semantics. > > This extension of the range does not restrict existing configurations > (quite the opposite). This may affect setups where weights >1000 were > attempted to be set but failed with the default 100. Such cgroups would > attain their intended weight now. This is a changed behavior but it > rectifies the situation (similar intention to the commit 69d7fde5909b > ("blkcg: use CGROUP_WEIGHT_* scale for io.weight on the unified > hierarchy") for CFQ formerly (and v2 only)). > > Additionally, the changed range does not imply all IO workloads can be > really controlled to achieve the widest possible ratio 1:10^4. > > Signed-off-by: Michal Koutný <mkoutny@suse.com> Looks fine to me. Acked-by: Tejun Heo <tj@kernel.org> Thanks. -- tejun ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: BFQ cgroup weights range @ 2021-08-27 8:33 ` Paolo Valente 0 siblings, 0 replies; 6+ messages in thread From: Paolo Valente @ 2021-08-27 8:33 UTC (permalink / raw) To: Tejun Heo; +Cc: Michal Koutný, Jens Axboe, linux-block, Jan Kara, cgroups > Il giorno 26 ago 2021, alle ore 19:25, Tejun Heo <tj@kernel.org> ha scritto: > > On Thu, Aug 26, 2021 at 03:12:12PM +0200, Michal Koutný wrote: >> On Tue, Aug 24, 2021 at 02:51:47PM +0200, Paolo Valente <paolo.valente@linaro.org> wrote: >>> BFQ inherited these constants when we forked it from CFQ. I'm ok with >>> increasing max weight to 10000. I only wonder whether this would >>> break some configuration, as the currently maximum weight would not be >>> the maximum weight any longer. >> >> Thanks for the reply. Let me form the idea as a patch (and commit >> message) and discuss based on that if needed (+ccrosspost into cgroups >> ML). >> >> -- >8 -- >> From: Michal Koutný <mkoutny@suse.com> >> Subject: [PATCH] block, bfq: Accept symmetric weight adjustments >> >> The allowed range for BFQ weights is currently 1..1000 with 100 being >> the default. There is no apparent reason to not accept weight >> adjustments of same ratio on both sides of the default. This change >> makes the attribute domain consistent with other cgroup (v2) knobs with >> the weight semantics. >> >> This extension of the range does not restrict existing configurations >> (quite the opposite). This may affect setups where weights >1000 were >> attempted to be set but failed with the default 100. Such cgroups would >> attain their intended weight now. This is a changed behavior but it >> rectifies the situation (similar intention to the commit 69d7fde5909b >> ("blkcg: use CGROUP_WEIGHT_* scale for io.weight on the unified >> hierarchy") for CFQ formerly (and v2 only)). >> >> Additionally, the changed range does not imply all IO workloads can be >> really controlled to achieve the widest possible ratio 1:10^4. >> >> Signed-off-by: Michal Koutný <mkoutny@suse.com> > > Looks fine to me. > > Acked-by: Tejun Heo <tj@kernel.org> > Acked-by: Paolo Valente <paolo.valente@linaro.org> Thanks for this improvement, Paolo > Thanks. > > -- > tejun ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: BFQ cgroup weights range @ 2021-08-27 8:33 ` Paolo Valente 0 siblings, 0 replies; 6+ messages in thread From: Paolo Valente @ 2021-08-27 8:33 UTC (permalink / raw) To: Tejun Heo Cc: Michal Koutný, Jens Axboe, linux-block, Jan Kara, cgroups-u79uwXL29TY76Z2rM5mHXA > Il giorno 26 ago 2021, alle ore 19:25, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> ha scritto: > > On Thu, Aug 26, 2021 at 03:12:12PM +0200, Michal Koutný wrote: >> On Tue, Aug 24, 2021 at 02:51:47PM +0200, Paolo Valente <paolo.valente-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote: >>> BFQ inherited these constants when we forked it from CFQ. I'm ok with >>> increasing max weight to 10000. I only wonder whether this would >>> break some configuration, as the currently maximum weight would not be >>> the maximum weight any longer. >> >> Thanks for the reply. Let me form the idea as a patch (and commit >> message) and discuss based on that if needed (+ccrosspost into cgroups >> ML). >> >> -- >8 -- >> From: Michal Koutný <mkoutny-IBi9RG/b67k@public.gmane.org> >> Subject: [PATCH] block, bfq: Accept symmetric weight adjustments >> >> The allowed range for BFQ weights is currently 1..1000 with 100 being >> the default. There is no apparent reason to not accept weight >> adjustments of same ratio on both sides of the default. This change >> makes the attribute domain consistent with other cgroup (v2) knobs with >> the weight semantics. >> >> This extension of the range does not restrict existing configurations >> (quite the opposite). This may affect setups where weights >1000 were >> attempted to be set but failed with the default 100. Such cgroups would >> attain their intended weight now. This is a changed behavior but it >> rectifies the situation (similar intention to the commit 69d7fde5909b >> ("blkcg: use CGROUP_WEIGHT_* scale for io.weight on the unified >> hierarchy") for CFQ formerly (and v2 only)). >> >> Additionally, the changed range does not imply all IO workloads can be >> really controlled to achieve the widest possible ratio 1:10^4. >> >> Signed-off-by: Michal Koutný <mkoutny-IBi9RG/b67k@public.gmane.org> > > Looks fine to me. > > Acked-by: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> > Acked-by: Paolo Valente <paolo.valente-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> Thanks for this improvement, Paolo > Thanks. > > -- > tejun ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-08-27 8:33 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-08-24 10:56 BFQ cgroup weights range Michal Koutný 2021-08-24 12:51 ` Paolo Valente 2021-08-26 13:12 ` Michal Koutný 2021-08-26 17:25 ` Tejun Heo 2021-08-27 8:33 ` Paolo Valente 2021-08-27 8:33 ` Paolo Valente
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