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Wed, 14 Jan 2026 03:08:45 -0800 (PST) From: Tang Yizhou X-Google-Original-From: Tang Yizhou To: tj@kernel.org, corbet@lwn.net, axboe@kernel.dk, hch@lst.de Cc: cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Tang Yizhou Subject: [PATCH] docs: Fix blk-iolatency peer throttling description Date: Wed, 14 Jan 2026 19:08:37 +0800 Message-ID: <20260114110837.84126-1-yizhou.tang@shopee.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Tang Yizhou 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 Acked-by: Michal Koutn=C3=BD --- 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 =20 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 t= he -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. =20 The limits are only applied at the peer level in the hierarchy. This mean= s that in the diagram below, only groups A, B, and C will influence each other, a= nd @@ -2265,8 +2266,9 @@ How IO Latency Throttling Works =20 io.latency is work conserving; so as long as everybody is meeting their la= tency 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 i= tself. -This throttling takes 2 forms: +target it begins throttling any peer group that has a higher target than i= tself, +as well as any peer group without a latency target. This throttling takes 2 +forms: =20 - 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 --=20 2.43.0