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Date: Tue, 6 Feb 2001 20:57:13 +0100 (CET)
From: Ingo Molnar <mingo@elte.hu>
Reply-To: <mingo@elte.hu>
To: Ben LaHaise <bcrl@redhat.com>
Cc: Linus Torvalds <torvalds@transmeta.com>,
        "Stephen C. Tweedie" <sct@redhat.com>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>,
        Manfred Spraul <manfred@colorfullife.com>, Steve Lord <lord@sgi.com>,
        Linux Kernel List <linux-kernel@vger.kernel.org>,
        <kiobuf-io-devel@lists.sourceforge.net>,
        Ingo Molnar <mingo@redhat.com>
Subject: Re: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait
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On Tue, 6 Feb 2001, Ben LaHaise wrote:

> This small correction is the crux of the problem: if it blocks, it
> takes away from the ability of the process to continue doing useful
> work.  If it returns -EAGAIN, then that's okay, the io will be
> resubmitted later when other disk io has completed.  But, it should be
> possible to continue servicing network requests or user io while disk
> io is underway.

typical blocking point is waiting for page completion, not
__wait_request(). But, this is really not an issue, NR_REQUESTS can be
increased anytime. If NR_REQUESTS is large enough then think of it as the
'absolute upper limit of doing IO', and think of the blocking as 'the
kernel pulling the brakes'.

[overhead of 512-byte bhs in the raw IO code is an artificial problem of
the raw IO code.]

	Ingo

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