[PATCH v2 4/4] net: apply __GFP_NO_AUTOINIT to AF_UNIX sk_buff allocations

[Alexander Potapenko]

On Fri, May 17, 2019 at 10:49 AM Alexander Potapenko <glider at google.com> wrote:
>
> On Fri, May 17, 2019 at 2:26 AM Kees Cook <keescook at chromium.org> wrote:
> >
> > On Thu, May 16, 2019 at 09:53:01AM -0700, Kees Cook wrote:
> > > On Tue, May 14, 2019 at 04:35:37PM +0200, Alexander Potapenko wrote:
> > > > Add sock_alloc_send_pskb_noinit(), which is similar to
> > > > sock_alloc_send_pskb(), but allocates with __GFP_NO_AUTOINIT.
> > > > This helps reduce the slowdown on hackbench in the init_on_alloc mode
> > > > from 6.84% to 3.45%.
> > >
> > > Out of curiosity, why the creation of the new function over adding a
> > > gfp flag argument to sock_alloc_send_pskb() and updating callers? (There
> > > are only 6 callers, and this change already updates 2 of those.)
> > >
> > > > Slowdown for the initialization features compared to init_on_free=0,
> > > > init_on_alloc=0:
> > > >
> > > > hackbench, init_on_free=1:  +7.71% sys time (st.err 0.45%)
> > > > hackbench, init_on_alloc=1: +3.45% sys time (st.err 0.86%)
> >
> > So I've run some of my own wall-clock timings of kernel builds (which
> > should be an pretty big "worst case" situation, and I see much smaller
> > performance changes:
> How many cores were you using? I suspect the numbers may vary a bit
> depending on that.
> > everything off
> >         Run times: 289.18 288.61 289.66 287.71 287.67
> >         Min: 287.67 Max: 289.66 Mean: 288.57 Std Dev: 0.79
> >                 baseline
> >
> > init_on_alloc=1
> >         Run times: 289.72 286.95 287.87 287.34 287.35
> >         Min: 286.95 Max: 289.72 Mean: 287.85 Std Dev: 0.98
> >                 0.25% faster (within the std dev noise)
> >
> > init_on_free=1
> >         Run times: 303.26 301.44 301.19 301.55 301.39
> >         Min: 301.19 Max: 303.26 Mean: 301.77 Std Dev: 0.75
> >                 4.57% slower
> >
> > init_on_free=1 with the PAX_MEMORY_SANITIZE slabs excluded:
> >         Run times: 299.19 299.85 298.95 298.23 298.64
> >         Min: 298.23 Max: 299.85 Mean: 298.97 Std Dev: 0.55
> >                 3.60% slower
> >
> > So the tuning certainly improved things by 1%. My perf numbers don't
> > show the 24% hit you were seeing at all, though.
> Note that 24% is the _sys_ time slowdown. The wall time slowdown seen
> in this case was 8.34%
I've collected more stats running QEMU with different numbers of cores.
The slowdown values of init_on_free compared to baseline are:
2 CPUs - 5.94% for wall time (20.08% for sys time)
6 CPUs - 7.43% for wall time (23.55% for sys time)
12 CPUs - 8.41% for wall time (24.25% for sys time)
24 CPUs - 9.49% for wall time (17.98% for sys time)

I'm building a defconfig of some fixed KMSAN tree with Clang, but that
shouldn't matter much.

> > > In the commit log it might be worth mentioning that this is only
> > > changing the init_on_alloc case (in case it's not already obvious to
> > > folks). Perhaps there needs to be a split of __GFP_NO_AUTOINIT into
> > > __GFP_NO_AUTO_ALLOC_INIT and __GFP_NO_AUTO_FREE_INIT? Right now
> > > __GFP_NO_AUTOINIT is only checked for init_on_alloc:
> >
> > I was obviously crazy here. :) GFP isn't present for free(), but a SLAB
> > flag works (as was done in PAX_MEMORY_SANITIZE). I'll send the patch I
> > used for the above timing test.
> >
> > --
> > Kees Cook
>
>
>
> --
> Alexander Potapenko
> Software Engineer
>
> Google Germany GmbH
> Erika-Mann-Straße, 33
> 80636 München
>
> Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg



-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg