[PATCH] docs: Fix blk-iolatency peer throttling description

[PATCH] docs: Fix blk-iolatency peer throttling description

[Tang Yizhou]

From: Tang Yizhou <yizhou.tang@shopee.com>

The current text states that peers with a lower latency target are
throttled, which is the opposite of the actual behavior. In fact,
blk-iolatency throttles peer groups with a higher latency target in order
to protect the more latency-sensitive group.

In addition, peer groups without a configured latency target are also
throttled, as they are treated as lower priority compared to groups with
explicit latency requirements.

Update the documentation to reflect the correct throttling behavior.

Signed-off-by: Tang Yizhou <yizhou.tang@shopee.com>
---
 Documentation/admin-guide/cgroup-v2.rst | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 7f5b59d95fce..d6f7ef08b67d 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2238,8 +2238,9 @@ IO Latency
 
 This is a cgroup v2 controller for IO workload protection.  You provide a group
 with a latency target, and if the average latency exceeds that target the
-controller will throttle any peers that have a lower latency target than the
-protected workload.
+controller will throttle any peers that have a higher latency target than the
+protected workload, as well as peers that do not have a latency target
+configured.
 
 The limits are only applied at the peer level in the hierarchy.  This means that
 in the diagram below, only groups A, B, and C will influence each other, and
@@ -2265,8 +2266,9 @@ How IO Latency Throttling Works
 
 io.latency is work conserving; so as long as everybody is meeting their latency
 target the controller doesn't do anything.  Once a group starts missing its
-target it begins throttling any peer group that has a higher target than itself.
-This throttling takes 2 forms:
+target it begins throttling any peer group that has a higher target than itself,
+as well as any peer group without a latency target. This throttling takes 2
+forms:
 
 - Queue depth throttling.  This is the number of outstanding IO's a group is
   allowed to have.  We will clamp down relatively quickly, starting at no limit
-- 
2.43.0

Re: [PATCH] docs: Fix blk-iolatency peer throttling description

[Michal Koutný]

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On Wed, Jan 14, 2026 at 07:08:37PM +0800, Tang Yizhou <yizhou.tang@shopee.com> wrote:
> From: Tang Yizhou <yizhou.tang@shopee.com>
> 
> The current text states that peers with a lower latency target are
> throttled, which is the opposite of the actual behavior. In fact,
> blk-iolatency throttles peer groups with a higher latency target in order
> to protect the more latency-sensitive group.
> 
> In addition, peer groups without a configured latency target are also
> throttled, as they are treated as lower priority compared to groups with
> explicit latency requirements.
> 
> Update the documentation to reflect the correct throttling behavior.
> 
> Signed-off-by: Tang Yizhou <yizhou.tang@shopee.com>
> ---
>  Documentation/admin-guide/cgroup-v2.rst | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)

Not a big deal but it could've been confusing.


Acked-by: Michal Koutný <mkoutny@suse.com>

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Re: [PATCH] docs: Fix blk-iolatency peer throttling description

[Tang Yizhou]

On Tue, Jan 20, 2026 at 9:37 PM Michal Koutný <mkoutny@suse.com> wrote:
>
> On Wed, Jan 14, 2026 at 07:08:37PM +0800, Tang Yizhou <yizhou.tang@shopee.com> wrote:
> > From: Tang Yizhou <yizhou.tang@shopee.com>
> >
> > The current text states that peers with a lower latency target are
> > throttled, which is the opposite of the actual behavior. In fact,
> > blk-iolatency throttles peer groups with a higher latency target in order
> > to protect the more latency-sensitive group.
> >
> > In addition, peer groups without a configured latency target are also
> > throttled, as they are treated as lower priority compared to groups with
> > explicit latency requirements.
> >
> > Update the documentation to reflect the correct throttling behavior.
> >
> > Signed-off-by: Tang Yizhou <yizhou.tang@shopee.com>
> > ---
> >  Documentation/admin-guide/cgroup-v2.rst | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
>
> Not a big deal but it could've been confusing.
>
>
> Acked-by: Michal Koutný <mkoutny@suse.com>

Hi Jon, just checking in, do you think this patch is ready to be merged?

Best regards,
Yi

Re: [PATCH] docs: Fix blk-iolatency peer throttling description

[Jonathan Corbet]

Tang Yizhou <yizhou.tang@shopee.com> writes:

> On Tue, Jan 20, 2026 at 9:37 PM Michal Koutný <mkoutny@suse.com> wrote:
>>
>> On Wed, Jan 14, 2026 at 07:08:37PM +0800, Tang Yizhou <yizhou.tang@shopee.com> wrote:
>> > From: Tang Yizhou <yizhou.tang@shopee.com>
>> >
>> > The current text states that peers with a lower latency target are
>> > throttled, which is the opposite of the actual behavior. In fact,
>> > blk-iolatency throttles peer groups with a higher latency target in order
>> > to protect the more latency-sensitive group.
>> >
>> > In addition, peer groups without a configured latency target are also
>> > throttled, as they are treated as lower priority compared to groups with
>> > explicit latency requirements.
>> >
>> > Update the documentation to reflect the correct throttling behavior.
>> >
>> > Signed-off-by: Tang Yizhou <yizhou.tang@shopee.com>
>> > ---
>> >  Documentation/admin-guide/cgroup-v2.rst | 10 ++++++----
>> >  1 file changed, 6 insertions(+), 4 deletions(-)
>>
>> Not a big deal but it could've been confusing.
>>
>>
>> Acked-by: Michal Koutný <mkoutny@suse.com>
>
> Hi Jon, just checking in, do you think this patch is ready to be merged?

Tejun usually takes cgroup-related docs changes directly, so I was
deferring on this one.  If the preference is for it to go through the
docs tree I can certainly pick it up.

Thanks,

jon