Messages in this thread | | | Date | Wed, 14 Jun 2006 12:10:16 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH -mm] i386: cpu_relax() smp.c |
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Andreas Mohr wrote:
>Hi, > >On Mon, Jun 12, 2006 at 08:37:43PM +0200, Andreas Mohr wrote: > >>Hi all, >> >>while reviewing 2.6.17-rc6-mm1, I found some places that might >>want to make use of cpu_relax() in order to not block secondary >>pipelines while busy-polling (probably especially useful on SMT CPUs): >> > >OK, no replies arguing against anything, thus patch follow-up. ;) >(no. 1 of 3) >
The other two look fine. This one should remove the mb(). cpu_relax IIRC already includes a barrier(), and we are not concerned about consistency here, only coherency, which the hardware takes care of for us.
The flush_cpumask is guaranteed to be cleared *after* all other variables (eg. flush_mm) have been used... that happens in the IPI handler of course.
Aside, if we *were* worried about consistency here, smp_mb would have been the more correct barrier to use.
> >Signed-off-by: Andreas Mohr <andi@lisas.de> > > >diff -urN linux-2.6.17-rc6-mm2.orig/arch/i386/kernel/smp.c linux-2.6.17-rc6-mm2.my/arch/i386/kernel/smp.c >--- linux-2.6.17-rc6-mm2.orig/arch/i386/kernel/smp.c 2006-06-08 10:38:04.000000000 +0200 >+++ linux-2.6.17-rc6-mm2.my/arch/i386/kernel/smp.c 2006-06-13 19:33:22.000000000 +0200 >@@ -388,9 +388,11 @@ > */ > send_IPI_mask(cpumask, INVALIDATE_TLB_VECTOR); > >- while (!cpus_empty(flush_cpumask)) >+ while (!cpus_empty(flush_cpumask)) { >+ cpu_relax(); > /* nothing. lockup detection does not belong here */ > mb(); >+ } > > flush_mm = NULL; > flush_va = 0; >
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