linux-kernel - Re: [PATCH -next RFC v3 0/8] improve tag allocation under heavy load

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Message-ID: <450b5ab6-fb82-06dc-2a11-e0b464901c74@acm.org>
Date:   Sun, 24 Apr 2022 20:09:01 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Yu Kuai <yukuai3@...wei.com>, axboe@...nel.dk,
        andriy.shevchenko@...ux.intel.com, john.garry@...wei.com,
        ming.lei@...hat.com, qiulaibin@...wei.com
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com
Subject: Re: [PATCH -next RFC v3 0/8] improve tag allocation under heavy load

On 4/15/22 03:10, Yu Kuai wrote:
> The single io performance(randwrite):
> 
> | bs       | 128k | 256k | 512k | 1m   | 1280k | 2m   | 4m   |
> | -------- | ---- | ---- | ---- | ---- | ----- | ---- | ---- |
> | bw MiB/s | 20.1 | 33.4 | 51.8 | 67.1 | 74.7  | 82.9 | 82.9 |

Although the above data is interesting, it is not sufficient. The above 
data comes from a setup with a single hard disk. There are many other 
configurations that are relevant (hard disk array, high speed NVMe, QD=1 
USB stick, ...) but for which no conclusions can be drawn from the above 
data.

Another question is whether the approach of this patch series is the 
right approach? I would expect that round-robin wakeup of waiters would 
be ideal from a fairness point of view. However, there are patches in 
this patch series that guarantee that wakeup of tag waiters won't happen 
in a round robin fashion.

Thanks,

Bart.