linux-kernel - Re: Can context switches be faster?

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Message-ID: <45302BE0.7040400@goop.org>
Date:	Fri, 13 Oct 2006 17:14:24 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andreas Mohr <andi@...x01.fht-esslingen.de>
CC:	John Richard Moser <nigelenki@...cast.net>,
	Chris Friesen <cfriesen@...tel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Can context switches be faster?

Andreas Mohr wrote:
> OK, so since we've now amply worked out in this thread that TLB/cache flushing
> is a real problem for context switching management, would it be possible to
> smartly reorder processes on the runqueue (probably works best with many active
> processes with the same/similar priority on the runqueue!) to minimize
> TLB flushing needs due to less mm context differences of adjacently scheduled
> processes?
> (i.e. don't immediately switch from user process 1 to user process 2 and
> back to 1 again, but always try to sort some kernel threads in between
> to avoid excessive TLB flushing)
>   

It does.  The kernel will (slightly) prefer to switch between two 
threads sharing an address space over switching to a different address 
space.  (Hm, at least it used to, but I can't see where that happens now.)

    J
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