linux-kernel - Re: [PATCH] proc: faster /proc/*/status

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Date:	Sun, 7 Aug 2016 09:59:47 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk
Subject: Re: [PATCH] proc: faster /proc/*/status

> And then what? Parsing format string is still be there.

Perhaps could have a fast path for simple cases.

> 
> This is first line of profile of the first function (format_decode)
> 
>        │     static noinline_for_stack
>        │     int format_decode(const char *fmt, struct printf_spec *spec)
>        │     {
>  10.38 │       push   %rbp			<===
>   1.07 │       mov    %rsp,%rbp
>   1.09 │       push   %r12
>   4.51 │       mov    %rsi,%r12
>   1.40 │       push   %rbx
>   1.86 │       mov    %rdi,%rbx
>        │       sub    $0x8,%rsp
> 
> It is so bloated that gcc needs to be asked to not screw up with stack
> size.

What happens when you drop all the noinlines for this? I assume
this would alread make it faster. And now that we have bigger
stacks we can likely tolerate it.


-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.