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Fri, 13 Nov 2026 08:55:23 +0000 (GMT) Received: from [9.123.7.57] (unknown [9.123.7.57]) by smtpav01.dal12v.mail.ibm.com (Postfix) with ESMTP; Fri, 13 Nov 2026 08:55:23 +0000 (GMT) Message-ID: <0975a9ae-d73f-4592-a715-55a52b6e143c@linux.ibm.com> Date: Fri, 13 Nov 2026 14:25:22 +0530 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] block: don't request a module for the none elevator To: Qiliang Yuan , Jens Axboe , Damien Le Moal , Ming Lei , Hannes Reinecke Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261111-bug-block-elevator-unchanged-v1-0-583198bd4e21@linux.dev> <20261111-bug-block-elevator-unchanged-v1-1-583198bd4e21@linux.dev> Content-Language: en-US From: Nilay Shroff In-Reply-To: <20261111-bug-block-elevator-unchanged-v1-1-583198bd4e21@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: qFdREogmOjTAFe1sL-GsdHCjrDoMFa-I X-Authority-Analysis: v=2.4 cv=PeVqFShd c=1 sm=1 tr=0 ts=6af6d080 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=zJRp6_cAMcgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=loaMudsPnU6qzrEnzdwA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: Fgx7GP9KWKvkNyFWcFy9V4nxM4FttGEE X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTEzMDAzNCBTYWx0ZWRfX5HQxlKiJR/iB w79RuluHNHy2gYTf8egkUsPcVXbl3QS54IxSH3bOSZWJ9OWjOoRdsDlca5niRZK51r5tBK7o9W/ aM4ieKCE/Il0LaAKmzGprVZrbqexVXzF0s7Hk88OVR21Zep/wKuCXQTBWMroFr6iTuvLhtUg3Xj h8ZVu0klPp1sqfnbH+FiH9xdVMC6HKmX/aDjydWSq8JNkUQHmoA7pNNau357Qj7T59P87w0c2Ia kmUfIymoUb1d0eDckO/4F0m0TgQILAEwIz6o63Xwu/PYW9vthErFO1Oojc5VAy+Tlv5ru9HXKfr j7nXxoMadYL/8A7fLo4SRvTqWFLqbQ92gwkt/Z3QaBMW3FZb6Ac3afecTuUp2oNpX2KEZWsTOHA +KdKufnIot19z1Kvdzbczd8VCY7lz5iA64Y7YMqhU+OwP6vH8gYZHh8vYAK8amxF3DU56JCHJ0t gx8l2WZJRAiqbkX5mvA== X-Proofpoint-Spam-Info: AW1haW4tMjYxMTEzMDAzNCBTYWx0ZWRfX0ErzZ6ce/1JS H754sx9EOHifSw+MfD09q4wh2tdDLeFuwb3iX0Vr1C7kVLYXSERv2L88GhJ6a8ADxs0iC6Zmnii vRGHb3AjsMi2WOl3FUu7C97S4wuz0m4= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-11-13_03,2026-11-11_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 phishscore=0 suspectscore=0 impostorscore=0 priorityscore=1501 lowpriorityscore=0 spamscore=0 malwarescore=0 clxscore=1015 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2611040001 definitions=main-2611130034 On 11/12/26 8:30 AM, Qiliang Yuan wrote: > elv_iosched_store() calls elv_iosched_load_module() for the requested > name before anything else, and loads "-iosched" if no elevator > type of that name is registered. "none" never is, so every write of > "none" to queue/scheduler ends up in request_module("none-iosched"). > > That runs a modprobe helper which can never find the module, and adds > several milliseconds to every switch to "none", including rewrites of > it by udev rules or tuning tools that set the scheduler on each disk. > > Return early for "none", like elevator_change() did before the module > loading moved into elv_iosched_load_module(). > > Writing queue/scheduler of a null_blk disk 20 times takes (median): > > operation before (ms) after (ms) change > none -> none 13.09 9.06 -31% > mq-deadline -> none 11.99 7.96 -34% > > Fixes: 734e1a8603128 ("block: Prevent deadlocks when switching elevators") > Signed-off-by: Qiliang Yuan Looks good to me: Reviewed-by: Nilay Shroff