From: Eric Wong <normalperson@yhbt.net>
To: kgio@librelist.com
Subject: Re: Re: [PATCH 3/3] add `#kgio_writev` and `#kgio_trywritev`
Date: Thu, 31 May 2012 21:10:52 +0000 [thread overview]
Message-ID: <20120531211052.GA24678@dcvr.yhbt.net> (raw)
In-Reply-To: CAL-rCA0=t5Sap=gr7P8wywv-GX+JOHQgRUg2sm0h0mNpALE-+A@mail.gmail.com
Юрий Соколов <funny.falcon@gmail.com> wrote:
> 2012/5/31 Eric Wong <normalperson@yhbt.net>
>
> > Юрий Соколов <funny.falcon@gmail.com> wrote:
> > > With many tiny strings substitution function from writev_compat.h is
> > faster.
> > > It seems that we should not always make call to system writev, but do it
> > > depending on a data shape. I'll try play with tomorrow.
> >
> > Yes, I expect writev_compat (or even naive write(ary.join)) to be faster
> > for tiny strings. Each iovec struct is 16-bytes on 64-bit, and this is
> > a _huge_ overhead on small strings. Setting up pointers/lengths ends up
> > being more expensive than copying the strings themselves.
> >
> > I think this optimization is best left to application authors to
> > decide (and documented as such).
> >
>
> Well, it is faster even with prepared iovec , and joining string on Ruby
> level is still
> slower.
> I think, it is easy to decide automatically whether to choose custom
> function or
> call library function considering average string size in a batch:
> when average string size is about 1000 bytes library function is certainly
> faster
> when strings are of 100 bytes then custom function is much faster
> Taking something around 500~700 bytes as threshold we could have a good
> performance in every case.
OK, numbers sound reasonable. Do you have benchmarks/examples for this?
> I don't think 16 bytes is very huge overhead considering that buffer is
> reused
> for every batch of strings.
I meant userspace needs to copy 16 bytes of metadata into the kernel
for every iovec.
next prev parent reply other threads:[~2012-05-31 21:10 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-30 13:56 [PATCH 1/3] Fix UnixClientReadServerWrite test class name Sokolov Yura 'funny-falcon
2012-05-30 13:56 ` [PATCH 2/3] use rb_str_subseq for tail string on write Sokolov Yura 'funny-falcon
2012-05-30 18:57 ` Eric Wong
2012-05-30 19:29 ` Юрий Соколов
2012-05-30 13:56 ` [PATCH 3/3] add `#kgio_writev` and `#kgio_trywritev` Sokolov Yura 'funny-falcon
2012-05-30 19:55 ` Юрий Соколов
2012-05-30 20:38 ` Eric Wong
2012-05-31 6:16 ` Юрий Соколов
2012-05-31 21:10 ` Eric Wong [this message]
2012-05-30 20:39 ` Eric Wong
2012-05-31 6:26 ` Юрий Соколов
2012-05-31 21:14 ` Eric Wong
2012-05-31 21:56 ` Eric Wong
2012-05-31 9:00 ` Sokolov Yura 'funny-falcon
2012-05-31 21:19 ` Eric Wong
2012-06-01 6:14 ` Юрий Соколов
2012-06-01 7:55 ` Eric Wong
2012-06-01 9:42 ` [PATCH] " Sokolov Yura 'funny-falcon
2012-06-01 19:20 ` Eric Wong
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