Re: Re: [PATCH 3/3] add `#kgio_writev` and `#kgio_trywritev`

["Юрий Соколов" <funny.falcon@gmail.com>]

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.
I don't think 16 bytes is very huge overhead considering that buffer is
reused
for every batch of strings.