linux-kernel - Re: [patch v2] epoll use a single inode ...

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Message-ID: <45ED96A6.3000704@zytor.com>
Date:	Tue, 06 Mar 2007 08:28:22 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Eric Dumazet <dada1@...mosbay.com>
CC:	Davide Libenzi <davidel@...ilserver.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch v2] epoll use a single inode ...

Eric Dumazet wrote:
> 
> For epoll, I suspect this is harmless : Programs dont allocate epolls fd 
> every milli second, but at startup only.
> 
> For pipes/sockets, using a 64 bits would be problematic, because 
> sprintf() uses a divide for each digit. And a divide is slow. Ten 
> divides are *very* slow.
> 

That's true for *any* sprintf(), though.  sprintf() converts all its 
arguments to 64 bits.

However, this could be optimized.  I think right now sprintf() uses a 
generic divide-by-base, but a divide by 8 and 16 can of course be 
handled with a shift, and divide by 10 can be replaced with a 
multiplication by 0x1999999999999999ULL on most architectures.

	-hpa
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