Re: [PATCH] seq_file: delete small-value optimization

From	Joe Perches <joe@perches.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] seq_file: delete small-value optimization
Date	2017-05-18 01:30 +0200
Message-ID	<tIgyd-1fy-5@gated-at.bofh.it> (permalink)
References	<tI4x4-1Sb-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Wed, 2017-05-17 at 13:33 +0300, Alexey Dobriyan wrote:
> > Joe Perches wrote:
> > 
> > On Tue, 2017-05-16 at 23:42 +0300, Alexey Dobriyan wrote:
> > > num_to_str() optimizes printing small integers [0..9], so the same
> > > check higher in callchain is unnecessary.
> > 
> > Doesn't the optimization exists for the frequent use of 0
> > in seq output?  
> > 
> > These seq_put_decimal calls are now slightly more expensive.
> 
> That additional CALL instruction is hardly measurable so you're adding
> branch to skip branch in the next function.

It's not the call instruction.

num_to_str pushes the value first to stack
and then sets up a loop to copy those chars
to buffer.

The current code immediately pushes to buffer.

It's a fair amount of overhead.

Have you measured it?

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Re: [PATCH] seq_file: delete small-value optimization Alexey Dobriyan <adobriyan@gmail.com> - 2017-05-17 12:40 +0200
  Re: [PATCH] seq_file: delete small-value optimization Joe Perches <joe@perches.com> - 2017-05-18 01:30 +0200

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