Message-ID: <49318822.1070100@redhat.com>
Date: Sat, 29 Nov 2008 20:21:22 +0200
From: Avi Kivity <avi@redhat.com>
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To: Alexander van Heukelum <heukelum@mailshack.com>
CC: "H. Peter Anvin" <hpa@zytor.com>,
       Alexander van Heukelum <heukelum@fastmail.fm>, lguest@ozlabs.org,
       jeremy@xensource.com, LKML <linux-kernel@vger.kernel.org>,
       Mike Travis <travis@sgi.com>, Cyrill Gorcunov <gorcunov@gmail.com>,
       Steven Rostedt <srostedt@redhat.com>, Andi Kleen <andi@firstfloor.org>,
       Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [Lguest] [PATCH RFC/RFB] x86_64,	i386: interrupt dispatch changes
References: <20081104150729.GC21470@localhost> <20081104170501.GE29626@one.firstfloor.org> <1225822006.21441.1282961299@webmail.messagingengine.com> <20081104204400.GC10825@elte.hu> <1226243805.27361.1283784629@webmail.messagingengine.com> <49178E89.2000307@zytor.com> <492DC13F.8020009@redhat.com> <492DE3EF.8060507@zytor.com> <492E72D7.9060201@redhat.com> <20081128204809.GA17920@mailshack.com> <20081129154516.GA26579@mailshack.com>
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Alexander van Heukelum wrote:
> I now did the benchmarks for the same -rc6 with hpa's 4-byte stubs
> too. Same machine. It's significantly better than the other two
> options in terms of speed. It takes about 7% less cpu to handle
> the interrupts. (0.64% cpu instead of 0.69%.) I have to run now,
> I'll let interpreting the histogram to someone else ;).
>   

This is noise. 0.05% cpu on a 1GHz machine servicing 1000 interrupt/sec 
boils down to 500 cycles/interrupt.  These changes shouldn't amount to 
so much (and I doubt you have 1000 interrupts/sec with a single disk)..

I'm sorry, but the whole effort is misguided, in my opinion.  If you 
want to optimize, try reducing the number of interrupts that occur 
rather than saving a few cycles in the interrupt path.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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