linux-kernel - Re: cpu4096 + smp

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Message-ID: <20080729150546.GA5140@martell.zuzino.mipt.ru>
Date:	Tue, 29 Jul 2008 19:05:46 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Mike Travis <travis@....com>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: cpu4096 + smp_affinity breakage

On Tue, Jul 29, 2008 at 04:34:13PM +0200, Jiri Slaby wrote:
> I see cpu4096 branches in -tip. Do you know about /proc/irq/*/*smp_affinity 
> (irq_affinity_read_proc, default_affinity_read) breakage with NR_CPUS=4096? 
> Reading by `cat' from those files fails due to bitmap sent out is about 
> 1150 bytes, but cat provides only 1024B sized buffer. Can you think about 
> any fix for this?
>
> Using file offset and utilize only portion of that buffer returned to the 
> userspace will break atomicity I guess (does this matter?). If we get a 
> snapshot, it would get old if some reader breaks up. And if we use 
> per-reader buffer, we will be unable to free it. Any ideas?
>
> I think the same problem is for not-at-once-writes.

Time to ressurect my smp_affinity-as-seq-file patch which was dropped
for a stupid reason. 

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