linux-kernel - Re: [PATCH] poll: Avoid extra wakeups in select/poll

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Message-ID: <20090429091637.GA29874@elte.hu>
Date:	Wed, 29 Apr 2009 11:16:37 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	linux kernel <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	David Miller <davem@...emloft.net>, cl@...ux.com,
	jesse.brandeburg@...el.com, netdev@...r.kernel.org,
	haoki@...hat.com, mchan@...adcom.com, davidel@...ilserver.org
Subject: Re: [PATCH] poll: Avoid extra wakeups in select/poll


* Eric Dumazet <dada1@...mosbay.com> wrote:

> @@ -418,8 +429,16 @@ int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
>  				if (file) {
>  					f_op = file->f_op;
>  					mask = DEFAULT_POLLMASK;
> -					if (f_op && f_op->poll)
> +					if (f_op && f_op->poll) {
> +						if (wait) {
> +							wait->key = POLLEX_SET;
> +							if (in & bit)
> +								wait->key |= POLLIN_SET;
> +							if (out & bit)
> +								wait->key |= POLLOUT_SET;
> +						}
>  						mask = (*f_op->poll)(file, retval ? NULL : wait);
> +					}
>  					fput_light(file, fput_needed);
>  					if ((mask & POLLIN_SET) && (in & bit)) {
>  						res_in |= bit;

Please factor this whole 'if (file)' branch out into a helper. 
Typical indentation levels go from 1 to 3 tabs - 4 should be avoided 
if possible and 5 is pretty excessive already. This goes to eight.

	Ingo
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