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Re: [PATCH v1.1] Randomize memcpy benchmark addresses.
- From: Siddhesh Poyarekar <siddhesh at redhat dot com>
- To: Will Newton <will dot newton at linaro dot org>
- Cc: OndÅej BÃlka <neleai at seznam dot cz>, libc-alpha <libc-alpha at sourceware dot org>
- Date: Fri, 6 Sep 2013 10:48:06 +0530
- Subject: Re: [PATCH v1.1] Randomize memcpy benchmark addresses.
- Authentication-results: sourceware.org; auth=none
- References: <20130904163151 dot GB10358 at domone dot kolej dot mff dot cuni dot cz> <20130904165025 dot GA15899 at domone dot kolej dot mff dot cuni dot cz> <CANu=DmjT9Do_1rbVJUGmR=WqGZmwX+KWNvp1QDOQrij3L3q3Xg at mail dot gmail dot com> <20130905113241 dot GA5818 at domone dot kolej dot mff dot cuni dot cz> <CANu=Dmitq7qp8gXHb0Us_WuL0bD7u_RfM-ZiR=E1b4=Da8ozQQ at mail dot gmail dot com> <20130905141547 dot GA18090 at domone dot kolej dot mff dot cuni dot cz> <CANu=Dmjne9sfarWKSLt6XUau968BWzN+dA+zm3+u4vtYMUNxHA at mail dot gmail dot com>
On Thu, Sep 05, 2013 at 03:32:09PM +0100, Will Newton wrote:
> > Current benchmark prints results for 4 pairs of alignments. Please
> > explain why do you thing that best and worst case are among them.
>
> I don't think the current tests test all the necessary alignments but
> that is a separate issue from whether or not we should print the
> benchmarked alignment. For example, if a memcpy implementation has an
> average case performance that is equal to another across a range of
> random alignments it may have quite different performance
> characteristics with various specific alignments of buffers. I think
> this is something that is useful to be able to see.
I agree. I have mentioned in the past too that while average case
performance numbers are useful, it doesn't make sense to get rid of
data that is already there and is quite important, which is
performance characteristics for specific alignments. The choice of
alignments is another question and we could probably have a separate
patch to improve that.
Siddhesh