linux-kernel - Re: [PATCH v2] Pre-emption control for userspace

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Message-ID: <20140325194724.GV22728@two.firstfloor.org>
Date:	Tue, 25 Mar 2014 20:47:24 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Khalid Aziz <khalid.aziz@...cle.com>
Cc:	Andi Kleen <andi@...stfloor.org>, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, peterz@...radead.org,
	akpm@...ux-foundation.org, andi.kleen@...el.com, rob@...dley.net,
	viro@...iv.linux.org.uk, oleg@...hat.com,
	gnomes@...rguk.ukuu.org.uk, riel@...hat.com, snorcht@...il.com,
	dhowells@...hat.com, luto@...capital.net, daeseok.youn@...il.com,
	ebiederm@...ssion.com, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v2] Pre-emption control for userspace

On Tue, Mar 25, 2014 at 12:47:52PM -0600, Khalid Aziz wrote:
> I am not sure if it would be practical and useful to integrate this
> into any of the standard locking interfaces, but I have not looked
> into it much either. My initial intent is to let individual apps
> decide if they could benefit from this interface and code it in if
> so since the interface is meant to be very simple. Do you see any of
> the standard locking interfaces where it would make sense to
> integrate this feature in, or are you thinking of creating a new
> interface?

It would probably make sense to use by default with glibc adaptive mutexes.

> I am reluctant to make it too big since reading larger quantities
> from userspace will take longer and start to impact performance.
> Keeping shared data limited to 32-bits allows us to move it between
> userspace and kernel with one instruction.

You don't need to read/write more. Just reserve more so that it 
can be sensibly extended later.

The feature bits would only need to be written once when it is set up.


-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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