Re: BFQ cgroup weights range

Il giorno 26 ago 2021, alle ore 19:25, Tejun Heo [off-list ref] ha scritto:

On Thu, Aug 26, 2021 at 03:12:12PM +0200, Michal Koutný wrote:

quoted

On Tue, Aug 24, 2021 at 02:51:47PM +0200, Paolo Valente [off-list ref] wrote:

quoted

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 <redacted>

Acked-by: Paolo Valente <redacted>

Thanks for this improvement,
Paolo

Thanks.

-- 
tejun