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Thu, 2 Oct 2025 15:12:50 +0000 (GMT) Message-ID: Date: Thu, 2 Oct 2025 20:42:48 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 7/7] blk-mq: add documentation for new queue attribute async_dpeth To: Yu Kuai , axboe@kernel.dk, bvanassche@acm.org, ming.lei@redhat.com Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, yukuai3@huawei.com, yi.zhang@huawei.com, yangerkun@huawei.com, johnny.chenyi@huawei.com References: <20250930071111.1218494-1-yukuai1@huaweicloud.com> <20250930071111.1218494-8-yukuai1@huaweicloud.com> Content-Language: en-US From: Nilay Shroff In-Reply-To: <20250930071111.1218494-8-yukuai1@huaweicloud.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=Se/6t/Ru c=1 sm=1 tr=0 ts=68de9678 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=x6icFKpwvdMA:10 a=i0EeH86SAAAA:8 a=VwQbUJbxAAAA:8 a=8rCECXInrZZGTntQbewA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=cPQSjfK2_nFv0Q5t_7PE:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTI3MDAxMCBTYWx0ZWRfXw5hcvswR/o/t lpqK8UEbc5Z+/Au/RPbQhCTi+cLSrSub6h5kyVgE9+Qcdc7gqZH9XNOSe3KAkKLfhirKBNEbOc1 LPKPy6souPvo5kZ2qVFffYl3ki6ObaqSLxhdDZkFpqGx/HuzRvowOIxiSQwFesqQkdQENlN2Lv9 H18Vd/ytZw/ewyyNpK0qfm4gV0+oZvi1YJlyBQMgyqt5/MM6Xg+OZNQBlkq2keMb3je10m2NtZD yW6j3BBJoo/cM6lfYZJjeBzxBwwXejhMbtB67T4CnUA8KvjCUIE/S2vMkILG4bZMZN6XYgSmhDJ zQ2UntWP2zzqdelp9aAdSzMzbSMBYasxAPDkRR+KyhDEP1SHHLVjBRXZW+frWly8FOP4yCwFY3n 3GXRnWahnLLHd+4nedQjR8102Ollzg== X-Proofpoint-GUID: pprgsBV7M6uICuP4qURKZFqmJ4qAYKn_ X-Proofpoint-ORIG-GUID: pprgsBV7M6uICuP4qURKZFqmJ4qAYKn_ X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1117,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-10-02_05,2025-10-02_03,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 malwarescore=0 suspectscore=0 bulkscore=0 lowpriorityscore=0 clxscore=1015 phishscore=0 priorityscore=1501 adultscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2509150000 definitions=main-2509270010 On 9/30/25 12:41 PM, Yu Kuai wrote: > From: Yu Kuai > > Explain the attribute and the default value in different case. > > Signed-off-by: Yu Kuai > --- > Documentation/ABI/stable/sysfs-block | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/Documentation/ABI/stable/sysfs-block b/Documentation/ABI/stable/sysfs-block > index 0ed10aeff86b..09b9b3db9a1f 100644 > --- a/Documentation/ABI/stable/sysfs-block > +++ b/Documentation/ABI/stable/sysfs-block > @@ -609,6 +609,16 @@ Description: > enabled, and whether tags are shared. > > > +What: /sys/block//queue/async_depth > +Date: August 2025 > +Contact: linux-block@vger.kernel.org > +Description: > + [RW] This controls how many async requests may be allocated in the > + block layer. If elevator is none, then this value is nr_requests. > + By default, this value is 75% of nr_requests for bfq and kyber, > + abd nr_requests for mq-deadline. > + Hmm, it seems we need to further elaborate above documentation, seeing the way this new sysfs interface is playing out now for different I/O schedulers. I'd suggest rewriting this as follow (you may further modify/simplify it based on your taste, if needed): Description: [RW] Controls how many asynchronous requests may be allocated in the block layer. The value is always capped at nr_requests. When no elevator is active (none): - async_depth is always equal to nr_requests. For bfq scheduler: - By default, async_depth is set to 75% of nr_requests. Internal limits are then derived from this value: * Sync writes: limited to async_depth (≈75% of nr_requests). * Async I/O: limited to ~2/3 of async_depth (≈50% of nr_requests). If a bfq_queue is weight-raised: * Sync writes: limited to ~1/2 of async_depth (≈37% of nr_requests). * Async I/O: limited to ~1/4 of async_depth (≈18% of nr_requests). - If the user writes a custom value to async_depth, BFQ will recompute these limits proportionally based on the new value. For Kyber: - By default async_depth is set to 75% of nr_requests. - If the user writes a custom value to async_depth, then it override the default and directly control the limit for writes and async I/O. For mq-deadline: - By default async_depth is set to nr_requests. - If the user writes a custom value to async_depth, then it override the default and directly control the limit for writes and async I/O. Thanks, --Nilay