Re: [RFC][PATCH 00/16] sched: Core scheduling

[Mel Gorman]

On Fri, Feb 22, 2019 at 12:45:44PM +0000, Mel Gorman wrote:
> On Mon, Feb 18, 2019 at 09:49:10AM -0800, Linus Torvalds wrote:
> > On Mon, Feb 18, 2019 at 9:40 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > >
> > > However; whichever way around you turn this cookie; it is expensive and nasty.
> > 
> > Do you (or anybody else) have numbers for real loads?
> > 
> > Because performance is all that matters. If performance is bad, then
> > it's pointless, since just turning off SMT is the answer.
> > 
> 
> I tried to do a comparison between tip/master, ht disabled and this series
> putting test workloads into a tagged cgroup but unfortunately it failed
> 
> [  156.978682] BUG: unable to handle kernel NULL pointer dereference at 0000000000000058
> [  156.986597] #PF error: [normal kernel read fault]
> [  156.991343] PGD 0 P4D 0

When bodged around, one test survived (performance was crucified but the
benchmark is very synthetic). pgbench (test 2) paniced with a hard
lockup. Most of the console log was corrupted (unrelated to the patch)
but the relevant part is

[ 4587.419674] Call Trace:
[ 4587.419674]  _raw_spin_lock+0x1b/0x20
[ 4587.419675]  sched_core_balance+0x155/0x520
[ 4587.419675]  ? __switch_to_asm+0x34/0x70
[ 4587.419675]  __balance_callback+0x49/0xa0
[ 4587.419676]  __schedule+0xf15/0x12c0
[ 4587.419676]  schedule_idle+0x1e/0x40
[ 4587.419677]  do_idle+0x166/0x280
[ 4587.419677]  cpu_startup_entry+0x19/0x20
[ 4587.419678]  start_secondary+0x17a/0x1d0
[ 4587.419678]  secondary_startup_64+0xa4/0xb0
[ 4587.419679] Kernel panic - not syncing: Hard LOCKUP

-- 
Mel Gorman
SUSE Labs