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From: Denys Vlasenko <vda.linux@googlemail.com>
To: musl <musl@lists.openwall.com>
Subject: Re: Re: [PATCH] x86_64/memset: simple optimizations
Date: Tue, 10 Feb 2015 21:52:54 +0100	[thread overview]
Message-ID: <CAK1hOcOHNCjPmqE1uq=OCbpckXz-xFJx_gcQ4Q-TKHgKGVEP-Q@mail.gmail.com> (raw)
In-Reply-To: <20150210204342.GJ23507@brightrain.aerifal.cx>

On Tue, Feb 10, 2015 at 9:43 PM, Rich Felker <dalias@aerifal.cx> wrote:
> On Tue, Feb 10, 2015 at 09:27:17PM +0100, Denys Vlasenko wrote:
>> On Sat, Feb 7, 2015 at 2:06 PM, Rich Felker <dalias@aerifal.cx> wrote:
>> /* libc has incredibly messy way of doing this,
>>  * typically requiring -lrt. We just skip all this mess */
>> static void get_mono(struct timespec *ts)
>> {
>>         syscall(__NR_clock_gettime, CLOCK_MONOTONIC, ts);
>> }
>
> FWIW, this is a bad idea; you get syscall overhead in your
> measurements. If you just use clock_gettime (the function) you'll get
> vdso results (no syscall).

I repeat memset 32 times between reading timespamp.
Thus, even with "small" 20kb memset test
there are 640kb of writes to L1. This is bit enough
to make overhead insignificant.


  reply	other threads:[~2015-02-10 20:52 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1423258814-9045-1-git-send-email-vda.linux@googlemail.com>
     [not found] ` <20150207003535.GS23507@brightrain.aerifal.cx>
     [not found]   ` <CAK1hOcP8zCo843y0VhqMr6Wc0JtaD4V4V=TicLnmJ6SynBhmGw@mail.gmail.com>
     [not found]     ` <20150207130655.GW23507@brightrain.aerifal.cx>
2015-02-10 20:27       ` Denys Vlasenko
2015-02-10 20:43         ` Rich Felker
2015-02-10 20:52           ` Denys Vlasenko [this message]
2015-02-10 20:54             ` Rich Felker

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