Re: [PATCH RESEND] sched: prefer an idle cpu vs an idle sibling for BALANCE_WAKE

[Josef Bacik <jbacik@fb.com>]

On 07/06/2015 01:13 AM, Mike Galbraith wrote:
> Hm.  Piddling with pgbench, which doesn't seem to collapse into a
> quivering heap when load exceeds cores these days, deltas weren't all
> that impressive, but it does appreciate the extra effort a bit, and a
> bit more when clients receive it as well.
>
> If you test, and have time to piddle, you could try letting wake_wide()
> return 1 + sched_feat(WAKE_WIDE_IDLE) instead of adding only if wakee is
> the dispatcher.
>
> Numbers from my little desktop box.
>
> NO_WAKE_WIDE_IDLE
> postgres@homer:~> pgbench.sh
> clients 8       tps = 116697.697662
> clients 12      tps = 115160.230523
> clients 16      tps = 115569.804548
> clients 20      tps = 117879.230514
> clients 24      tps = 118281.753040
> clients 28      tps = 116974.796627
> clients 32      tps = 119082.163998   avg   117092.239   1.000
>
> WAKE_WIDE_IDLE
> postgres@homer:~> pgbench.sh
> clients 8       tps = 124351.735754
> clients 12      tps = 124419.673135
> clients 16      tps = 125050.716498
> clients 20      tps = 124813.042352
> clients 24      tps = 126047.442307
> clients 28      tps = 125373.719401
> clients 32      tps = 126711.243383   avg   125252.510   1.069   1.000
>
> WAKE_WIDE_IDLE (clients as well as server)
> postgres@homer:~> pgbench.sh
> clients 8       tps = 130539.795246
> clients 12      tps = 128984.648554
> clients 16      tps = 130564.386447
> clients 20      tps = 129149.693118
> clients 24      tps = 130211.119780
> clients 28      tps = 130325.355433
> clients 32      tps = 129585.656963   avg   129908.665   1.109   1.037
>

I have time for twiddling, we're carrying ye olde WAKE_IDLE until we get 
this solved upstream and then I'll rip out the old and put in the new, 
I'm happy to screw around until we're all happy.  I'll throw this in a 
kernel this morning and run stuff today.  Barring any issues with the 
testing infrastructure I should have results today.  Thanks,

Josef