linux-kernel - Re: [PATCH] blk-wbt: get back the missed wakeup from __wbt

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Message-ID: <677c8648-63fd-601c-b906-40a8502f9782@kernel.dk>
Date:   Fri, 24 Aug 2018 12:50:44 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Anchal Agarwal <anchalag@...n.com>
Cc:     fllinden@...zon.com, Jianchao Wang <jianchao.w.wang@...cle.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        anchalag@...zon.com
Subject: Re: [PATCH] blk-wbt: get back the missed wakeup from __wbt_done

On 8/24/18 12:12 PM, Anchal Agarwal wrote:
> That's totally fair. As compared to before the patch it was way too high
> and my test case wasn't even running due to the thunderign herd issues and
> queue re-ordering. Anyways as I also mentioned before 10 times 
> contention is not too bad since its not really affecting much the number of
> files read in my applciation. Also, you are right waking up N tasks seems 
> plausible. 

OK, I'm going to take that as a positive response. I'm going to propose
the last patch as the final addition in this round, since it does fix a
gap in the previous. And I do think that we need to wake as many tasks
as can make progress, otherwise we're deliberately running the device at
a lower load than we should.

> My application is somewhat similar to database workload. It does uses fsync 
> internally also. So what it does is it creates files of random sizes with 
> random contents. It stores the hash of those files in memory. During the 
> test it reads those files back from storage and checks their hashes. 

How many tasks are running for your test?

-- 
Jens Axboe