linux-kernel - Re: [PATCH 3/5] blk-mq: fix plugging in blk_sq_make

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Message-ID: <x497fss196b.fsf@segfault.boston.devel.redhat.com>
Date:	Fri, 01 May 2015 13:47:56 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Christoph Hellwig <hch@....de>
Cc:	Shaohua Li <shli@...com>, linux-kernel@...r.kernel.org,
	axboe@...com, neilb@...e.de
Subject: Re: [PATCH 3/5] blk-mq: fix plugging in blk_sq_make_request

Christoph Hellwig <hch@....de> writes:

>> -	if (use_plug && !blk_queue_nomerges(q) &&
>> +	if (likely(!is_flush_fua) && !blk_queue_nomerges(q) &&
>
> Please don't sprinkle likely annotations for no go reason.  Especially
> on metadata write heavy workloads (e.g. an NFS server) it might be very
> likely.

I have no problem getting rid of the likely, but I was mimicing the mq
case:

blk_mq_make_request:
        if (unlikely(is_flush_fua)) {
                blk_mq_bio_to_request(rq, bio);
                blk_insert_flush(rq);
                goto run_queue;
        }

So would you also want that unlikely removed?

Cheers,
Jeff
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