On Wed, Nov 21, 2018 at 09:51:19PM +0100, Jiri Kosina wrote: > On Wed, 21 Nov 2018, Tim Chen wrote: > > > Commit 53c613fe "x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation" > > turns on STIBP all the time. > > > > This causes large performance regression in many workloads. > > > > One case is perlbench in the SpecInt Rate 2006 test suite which shows a > > 21% reduction in throughput. > > There're also other reports of drop in performance on Python and PHP benchmarks: > > https://www.phoronix.com/scan.php?page=article&item=linux-420-bisect&num=2 > > > > STIBP on all the time should not be the default option. > > > > Turn off STIBP all the time for now till STIBP can be applied on > > a per task basis. > > > > Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> > > --- > > arch/x86/kernel/cpu/bugs.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c > > index c37e66e..21a8f39 100644 > > --- a/arch/x86/kernel/cpu/bugs.c > > +++ b/arch/x86/kernel/cpu/bugs.c > > @@ -332,7 +332,7 @@ static bool stibp_needed(void) > > if (!boot_cpu_has(X86_FEATURE_STIBP)) > > return false; > > > > - return true; > > + return false; > > } > > For -stable, which actually makes it to production, I already asked Greg > to drop it. It's in the latest stable -rc releases, and if all goes well, they will be released tomorrow. thanks, greg k-h
