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Date: Thu, 19 Nov 2009 14:16:34 +0000
From: Matthew Garrett <mjg59@srcf.ucam.org>
To: Kay Sievers <kay.sievers@vrfy.org>
Cc: David Zeuthen <david@fubar.dk>, linux-kernel@vger.kernel.org,
       axboe@kernel.dk, linux-hotplug@vger.kernel.org
Subject: Re: [PATCH] [RFC] Add support for uevents on block device idle
	changes
Message-ID: <20091119141634.GA311@srcf.ucam.org>
References: <20091118194053.GB12944@srcf.ucam.org> <ac3eb2510911181147ufeacb58u5194b0e1e5fd86d6@mail.gmail.com> <20091118195342.GA13627@srcf.ucam.org> <ac3eb2510911181203r1be5c3dajdacec94f196d550c@mail.gmail.com> <20091118200712.GA14026@srcf.ucam.org> <ac3eb2510911181306g221e8940xfbcf8b8e7fa9a56e@mail.gmail.com> <20091118213355.GA16630@srcf.ucam.org> <ac3eb2510911190309y6d0d8445wd907fc5664595c6f@mail.gmail.com> <20091119130107.GB20949@srcf.ucam.org> <ac3eb2510911190529p6810508fve4941f3077dfd3d9@mail.gmail.com>
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On Thu, Nov 19, 2009 at 02:29:29PM +0100, Kay Sievers wrote:
> On Thu, Nov 19, 2009 at 14:01, Matthew Garrett <mjg@redhat.com> wrote:
> > On Thu, Nov 19, 2009 at 12:09:30PM +0100, Kay Sievers wrote:
> >> On Wed, Nov 18, 2009 at 22:33, Matthew Garrett <mjg59@srcf.ucam.org> wrote:
> >> > My use cases are on the order of a second.
> >>
> >> Ok, what's the specific use case, which should be triggered after a
> >> second? I thought you were thinking about disk spindown or similar.
> >
> > The first is altering ALPM policy. ALPM will be initiated by the host if
> > the number of queued requests hits zero - if there's no hysteresis
> > implemented, then that can result in a significant performance hit. We
> > don't need /much/ hysteresis, but it's the difference between a 50%
> > performance hit and not having that.
> 
> Can't that logic live entirely in the kernel, instead of being a
> rather generic userspace event interface (with the current limitation
> to a single user)?

It could, but it seems a bit of a hack. It'd still also require the 
timer to be in the kernel, so we might as well expose that to userspace.

-- 
Matthew Garrett | mjg59@srcf.ucam.org
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