On Fri, May 17, 2019 at 10:49:03AM +0200, Alexander Potapenko wrote: > On Fri, May 17, 2019 at 2:26 AM Kees Cook <keescook@xxxxxxxxxxxx> 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. I was using 4. > > 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% Ah! Gotcha. Yeah, seems the impact for init_on_free is pretty variable. The init_on_alloc appears close to free, though. -- Kees Cook
