From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 8 Nov 2007 15:25:47 -0800 (PST) From: Christoph Lameter Subject: Re: Some interesting observations when trying to optimize vmstat handling In-Reply-To: <200711090007.43424.ak@suse.de> Message-ID: References: <200711090007.43424.ak@suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Andi Kleen Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mathieu Desnoyers List-ID: On Fri, 9 Nov 2007, Andi Kleen wrote: > > > 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) Well maybe we should change local_irq_save/restore in general? The result would be: if (!in_interrupt()) local_irq_disable() if (!in_interrupt()) local_irq_enable(); Somehow we need to remember that we disabled interrupts. Then it get more complicated. int interrupts_disabled = 0; if (!in_interrupt()) { local_irq_disable(): interrrupts_disabled = 1; } if (interrupts_disabled) local_irq_enable(); Not sure that this actually better. > 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. The statistics code surely does not rely on that. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org