Re: [PATCH] proc: speedup /proc/stat handling

[KAMEZAWA Hiroyuki]

On Fri, 20 Jan 2012 16:59:24 +0100
Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:

> On a typical 16 cpus machine, "cat /proc/stat" gives more than 4096
> bytes, and is slow :
> 
> # strace -T -o /tmp/STRACE cat /proc/stat | wc -c
> 5826
> # grep "cpu " /tmp/STRACE
> read(0, "cpu  1949310 19 2144714 12117253"..., 32768) = 5826 <0.001504>
> 
> 
> Thats partly because show_stat() must be called twice since initial
> buffer size is too small (4096 bytes for less than 32 possible cpus)
> 
> Fix this by :
> 
> 1) Taking into account nr_irqs in the initial buffer sizing.
> 
> 2) Using ksize() to allow better filling of initial buffer.
> 
> 3) Reduce the bloat on "intr ..." line :
>    Dont output trailing " 0" values at the end of irq range.
> 
> An alternative to 1) would be to remember the largest m->count reached
> in show_stat()
> 

nice catch. But how about using usual seq_file rather than single_open() ?
I just don't like multi-page buffer for this small file...very much.

A rough patch here, maybe optimization will not be enough. (IOW, this may be slow.)

==