linux-kernel - Re: Some interesting observations when trying to optimize vmstat handling

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Message-Id: <200711090007.43424.ak@suse.de>
Date:	Fri, 9 Nov 2007 00:07:42 +0100
From:	Andi Kleen <ak@...e.de>
To:	Christoph Lameter <clameter@....com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: Some interesting observations when trying to optimize vmstat handling


> There is an interrupt enable overhead of 48 cycles that would be good to
> be able to eliminate (Kernel code usually moves counter increments into
> a neighboring interrupt disable section so that __ function can be used).

Replace the push flags ; popf  with test $IFMASK,flags ; jz 1f; sti ; 1:
That will likely make it much faster (but also bigger) 

The only problem is that there might be some code who relies on 
restore_flags() restoring other flags that IF, but at least for interrupts
and local_irq_save/restore it should be fine to change.

-Andi

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