linux-kernel - Re: [patch 1/2] ufd v1 - unsequential O(1) fdmap core

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Date:	Mon, 4 Jun 2007 16:28:55 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ulrich Drepper <drepper@...hat.com>
Subject: Re: [patch 1/2] ufd v1 - unsequential O(1) fdmap core

On Mon, 4 Jun 2007 06:35:16 -0700 (PDT)
Davide Libenzi <davidel@...ilserver.org> wrote:

> On Mon, 4 Jun 2007, Eric Dumazet wrote:
> 
> > You add conditional branches on very hot spots.
> 
> Keep BS for the ones you argue usually, and that are not able to reply.
> You *still* two bitmaps, because allocation spaces are far apart. So the 
> "if" will still be there.

I actually read your patches and spent time to see the pros and cons.

If you dont need reviewers, please dont post your patches on lkml.

If I am not mistaken, you added a test in fget()/fget_light(), which is a known hot point for said huge processes.

fget() dont need to access the bitmap at all. Using fd_slots means less (50%) file pointers per cache line.

On my machines, there is a ratio of 100/1 in cpu time for fget(),fget_light() against get_unused_fd().

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