linux-kernel - Re: [PATCH] bfq: do try insert merge before bfq_init

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Date:   Sat, 15 Oct 2022 11:32:27 +0800
From:   Yuwei Guan <ssawgyw@...il.com>
To:     Jan Kara <jack@...e.cz>
Cc:     paolo.valente@...aro.org, axboe@...nel.dk,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yuwei.Guan@...krlife.com
Subject: Re: [PATCH] bfq: do try insert merge before bfq_init_rq() call


On 2022/10/14 22:50, Jan Kara wrote:
> On Thu 13-10-22 21:53:21, Yuwei Guan wrote:
>> It's useless to do bfq_init_rq(rq), if the rq can do merge first.
>>
>> In the patch 5f550ede5edf8, it moved to bfq_init_rq() before
>> blk_mq_sched_try_insert_merge(), but it's pointless,
>> as the fifo_time of next is not set yet,
>> and !list_empty(&next->queuelist) is 0, so it does not
>> need to reposition rq's fifo_time.
>>
>> And for the "hash lookup, try again" situation, as follow,
>> bfq_requests_merged() call can work normally.
>>
>> blk_mq_sched_try_insert_merge
>>    elv_attempt_insert_merge
>>      elv_rqhash_find
>>
>> Signed-off-by: Yuwei Guan <Yuwei.Guan@...krlife.com>
> OK, after some thinking I agree. How much testing has this patch got?
> Because I'd like to verify we didn't overlook something.
>
> 							Honza
Thanks for reviewing.
I tested it with fio seq read case like bellow,
then check blk trace and bfq log.

[global]
name=fio-seq-reads
filename=fio-seq-reads
rw=read
bs=16K
direct=1
numjobs=4

[file1]
size=32m
ioengine=psync

What kinds of test cases you perfer to do, I will deal with them,
or we verify this patch together, if you have free time. :)
>> ---
>>   block/bfq-iosched.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
>> index 7ea427817f7f..9845370a701c 100644
>> --- a/block/bfq-iosched.c
>> +++ b/block/bfq-iosched.c
>> @@ -6147,7 +6147,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
>>   		bfqg_stats_update_legacy_io(q, rq);
>>   #endif
>>   	spin_lock_irq(&bfqd->lock);
>> -	bfqq = bfq_init_rq(rq);
>> +
>>   	if (blk_mq_sched_try_insert_merge(q, rq, &free)) {
>>   		spin_unlock_irq(&bfqd->lock);
>>   		blk_mq_free_requests(&free);
>> @@ -6156,6 +6156,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
>>   
>>   	trace_block_rq_insert(rq);
>>   
>> +	bfqq = bfq_init_rq(rq);
>>   	if (!bfqq || at_head) {
>>   		if (at_head)
>>   			list_add(&rq->queuelist, &bfqd->dispatch);
>> -- 
>> 2.34.1
>>