linux-kernel - Re: [PATCH] aio: Skip timer for io

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Date:	Thu, 6 Nov 2014 14:41:19 -0500
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Fam Zheng <famz@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>, linux-aio@...ck.org,
	linux-fsdevel@...r.kernel.org, stefanha@...hat.com,
	pbonzini@...hat.com, lersek@...hat.com
Subject: Re: [PATCH] aio: Skip timer for io_getevents if timeout=0

Hi Fam,

On Thu, Nov 06, 2014 at 08:44:36PM +0800, Fam Zheng wrote:
> In this case, it is basically a polling. Let's not involve timer at all
> because that would hurt performance for application event loops.
> 
> In an arbitrary test I've done, io_getevents syscall elapsed time
> reduces from 50000+ nanoseconds to a few hundereds.

This looks quite reasonable.  I've applied this to my aio-next tree.

		-ben

> Signed-off-by: Fam Zheng <famz@...hat.com>
> ---
>  fs/aio.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/aio.c b/fs/aio.c
> index 84a7510..7c0b561 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -1221,8 +1221,12 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr,
>  	 * the ringbuffer empty. So in practice we should be ok, but it's
>  	 * something to be aware of when touching this code.
>  	 */
> -	wait_event_interruptible_hrtimeout(ctx->wait,
> -			aio_read_events(ctx, min_nr, nr, event, &ret), until);
> +	if (until.tv64 == 0)
> +		aio_read_events(ctx, min_nr, nr, event, &ret);
> +	else
> +		wait_event_interruptible_hrtimeout(ctx->wait,
> +				aio_read_events(ctx, min_nr, nr, event, &ret),
> +				until);
>  
>  	if (!ret && signal_pending(current))
>  		ret = -EINTR;
> -- 
> 1.9.3

-- 
"Thought is the essence of where you are now."
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