linux-kernel - Re: [PATCH v3] block: fix the problem of io

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Date:   Wed, 7 Jul 2021 18:46:50 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     brookxu <brookxu.cn@...il.com>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] block: fix the problem of io_ticks becoming smaller

On Tue, Jul 06, 2021 at 05:47:26AM +0800, brookxu wrote:
> From: Chunguang Xu <brookxu@...cent.com>
> 
> On the IO submission path, blk_account_io_start() may interrupt
> the system interruption. When the interruption returns, the value
> of part->stamp may have been updated by other cores, so the time
> value collected before the interruption may be less than part->
> stamp. So when this happens, we should do nothing to make io_ticks
> more accurate? For kernels less than 5.0, this may cause io_ticks
> to become smaller, which in turn may cause abnormal ioutil values.

Just be curious, is there any user visible difference with this change?

It can only be one issue if the stamp update crosses two jiffies, but
this event should be very unlikely, right?

Thanks, 
Ming