From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jack Steiner Date: Tue, 07 Mar 2006 17:24:29 +0000 Subject: Re: [patch] optimize flush_tlb_range on large numa box Message-Id: <20060307172428.GA2500@sgi.com> List-Id: References: <200603062212.k26MCsg16120@unix-os.sc.intel.com> In-Reply-To: <200603062212.k26MCsg16120@unix-os.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org On Mon, Mar 06, 2006 at 02:12:54PM -0800, Chen, Kenneth W wrote: > It was reported from a field customer that global spin lock ptcg_lock > is giving a lot of grief on munmap performance running on a large numa > machine. What appears to be a problem coming from flush_tlb_range(), > which currently unconditionally calls platform_global_tlb_purge(). > For some of the numa machines in existence today, this function is > mapped into ia64_global_tlb_purge(), which holds ptcg_lock spin lock > while executing ptc.ga instruction. > > Here is a patch that attempt to avoid global tlb purge whenever > possible. It will use local tlb purge as much as possible. Though the > conditions to use local tlb purge is pretty restrictive. One of the > side effect of having flush tlb range instruction on ia64 is that > kernel don't get a chance to clear out cpu_vm_mask. On ia64, this mask > is sticky and it will accumulate if process bounces around. Thus > diminishing the possible use of ptc.l. Thoughts? Patch looks good to me. There is some minor cleanup that can be done in the SN platform_global_tlb_purge function to take advantage of this patch. I'll do that later in a followup patch - the changes are NOT required for your patch to be accepted. I think clearing cpu_vm_mask is a good idea. I experimented with doing that by calling flush_tlb_mm() from the SN platform_global_tlb_purge function & got a big benefit. However, our workloads are atypical & I'm not sure the same algorithm is appropriate for all workloads. Additional measurements are needed. Acked-by: Jack Steiner > > > > Signed-off-by: Ken Chen > > --- ./arch/ia64/mm/tlb.c.orig 2006-03-05 12:21:27.400110815 -0800 > +++ ./arch/ia64/mm/tlb.c 2006-03-05 12:23:04.725304935 -0800 > @@ -156,17 +156,19 @@ flush_tlb_range (struct vm_area_struct * > nbits = purge.max_bits; > start &= ~((1UL << nbits) - 1); > > -# ifdef CONFIG_SMP > - platform_global_tlb_purge(mm, start, end, nbits); > -# else > preempt_disable(); > +#ifdef CONFIG_SMP > + if (mm != current->active_mm || cpus_weight(mm->cpu_vm_mask) != 1) { > + platform_global_tlb_purge(mm, start, end, nbits); > + preempt_enable(); > + return; > + } > +#endif > do { > ia64_ptcl(start, (nbits<<2)); > start += (1UL << nbits); > } while (start < end); > preempt_enable(); > -# endif > - > ia64_srlz_i(); /* srlz.i implies srlz.d */ > } > EXPORT_SYMBOL(flush_tlb_range); > > - > To unsubscribe from this list: send the line "unsubscribe linux-ia64" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Thanks Jack Steiner (steiner@sgi.com) 651-683-5302 Principal Engineer SGI - Silicon Graphics, Inc.