Re: [PATCH RESEND 1/3] initramfs: move unnecessary memcmp from hot path

[David Disseldorp <ddiss@suse.de>]

On Wed, 4 Aug 2021 12:57:16 +0000, Al Viro wrote:

> On Wed, Aug 04, 2021 at 11:31:29AM +0200, David Disseldorp wrote:
> > Ping, any feedback on this change?
> > 
> > I think it's a no brainer, but for kicks I ran a few unrealistic micro
> > benchmarks on my laptop. Extraction time for a cpio image with 1M+
> > directories improved by 5ms (pre: 14.614s, post: 14.609s), when averaged
> > across 20 runs of:
> >   qemu-system-x86_64 -machine accel=kvm -smp cpus=1 -m 10240 \
> >         -kernel ~/linux/arch/x86/boot/bzImage \
> >         -initrd ./initrds/gen_cpio.out \
> >         -append "initramfs_async=0 console=ttyS0 panic=0" -nographic \
> >         | awk '/Trying to unpack rootfs/ {start_ts = $2};
> >                /Freeing initrd memory/ {end_ts = $2}
> >                END {printf "%f\n", end_ts - start_ts}'  
> 
> What was the dispersion for those runs?

Too high for the 5ms to be considered statistically significant. Std
deviations were pre: 171ms, post: 214ms... <sigh> I'll redo this on a
proper test rig.

Cheers, David