linux-kernel - Re: [PATCH v2 3/4] block/elevator: choose none elevator for high IO concurrency ability disk

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Message-ID: <292f069e-023b-2f3c-6cae-0d133190749a@huaweicloud.com>
Date: Wed, 18 Dec 2024 09:28:30 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Bart Van Assche <bvanassche@....org>, Yu Kuai <yukuai1@...weicloud.com>,
 axboe@...nel.dk, akpm@...ux-foundation.org, ming.lei@...hat.com,
 yang.yang@...o.com, osandov@...com, paolo.valente@...aro.org
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 yi.zhang@...wei.com, yangerkun@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v2 3/4] block/elevator: choose none elevator for high IO
 concurrency ability disk

Hi,

在 2024/12/18 5:50, Bart Van Assche 写道:
> On 12/16/24 6:40 PM, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@...wei.com>
>>
>> The maximal default nr_requests is 256, and if disk can handle more than
>> 256 requests concurrently, use elevator in this case is useless, on the
>> one hand it limits the number of requests to 256, on the other hand,
>> it can't merge or sort IO because requests are dispatched to disk
>> immediately and the elevator is just empty.
>>
>> For example, for nvme megaraid with 512 queue_depth by default, we have
>> to change default elevator to none, otherwise deadline will lose a lot of
>> performance.
>>
>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
>> ---
>>   block/elevator.c | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/block/elevator.c b/block/elevator.c
>> index 7c3ba80e5ff4..4cce1e7c47d5 100644
>> --- a/block/elevator.c
>> +++ b/block/elevator.c
>> @@ -568,6 +568,17 @@ static struct elevator_type 
>> *elevator_get_default(struct request_queue *q)
>>           !blk_mq_is_shared_tags(q->tag_set->flags))
>>           return NULL;
>> +    /*
>> +     * If nr_queues will be less than disk ability, requests will be
>> +     * dispatched to disk immediately, it's useless to use elevator. 
>> User
>> +     * should set a bigger nr_requests or limit disk ability manually if
>> +     * they really want to use elevator.
>> +     */
>> +    if (q->queue_depth && q->queue_depth >= BLKDEV_DEFAULT_RQ * 2)
>> +        return NULL;
>> +    if (!q->queue_depth && q->tag_set->queue_depth >= 
>> BLKDEV_DEFAULT_RQ * 2)
>> +        return NULL;
>> +
>>       return elevator_find_get("mq-deadline");
>>   }
> 
> Shouldn't this patch be submitted separately since it is independent of
> the rest of the patches in this series?

Yes, this patch was added to this set by mistake. My bad. :(
I'm supposed to use the cleanup patch from v1 to replace this patch.

Thanks,
Kuai

> 
> Thanks,
> 
> Bart.
> 
> 
> .
>