linux-kernel - Re: [PATCH] Syslets - Fix cachemiss

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Message-ID: <20070531233946.GA12493@c2.user-mode-linux.org>
Date:	Thu, 31 May 2007 19:39:46 -0400
From:	Jeff Dike <jdike@...toit.com>
To:	Zach Brown <zach.brown@...cle.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	uml-devel <user-mode-linux-devel@...ts.sourceforge.net>
Subject: Re: [PATCH] Syslets - Fix cachemiss_thread return value

On Thu, May 31, 2007 at 03:07:16PM -0700, Zach Brown wrote:
> Can you explain what motivated you to send out this patch?
> 
> It used to return 0.  It was changed because, unlike the syslet
> syscalls, sys_io_submit() doesn't have a simple 0 value to indicate
> success.  The current implementation wants to return the number of iocbs
> that were processed, including the one which blocked, from the cachemiss
> thread.  So before calling into an operation it sets task_ret_ret() so
> that the cachemiss thread can return it if it takes over.
> task_ret_reg() is holding a return value that is being returned by the
> cachemiss thread on behalf of a sys_io_submit() which blocked.
> 
> When I made the change I didn't really audit its effect on the other
> paths.  I suppose it's time to do that, and you could help by telling me
> if you saw something bad happen :).

The bad thing was sys_async_exec returning -NOSYS every time a new
cachemiss thread was created.

Without this patch, you'll see sys_async_exec failures with either of
the demos I sent out.  Dunno about the existing ones, but I bet they do
the same.

				Jeff

-- 
Work email - jdike at linux dot intel dot com
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