Messages in this thread | | | Subject | Re: [pchecks v1 2/4] Use raw cpu ops for calls that would trigger with checks | From | Eric Dumazet <> | Date | Tue, 24 Sep 2013 05:45:04 -0700 |
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On Tue, 2013-09-24 at 09:32 +0200, Ingo Molnar wrote: > (netdev Cc:-ed) > > * Christoph Lameter <cl@linux.com> wrote: > > > These location triggered during testing with KVM. > > > > These are fetches without preemption off where we judged that > > to be more performance efficient or where other means of > > providing synchronization (BH handling) are available. > > > Index: linux/include/net/snmp.h > > =================================================================== > > --- linux.orig/include/net/snmp.h 2013-09-12 13:26:29.216103951 -0500 > > +++ linux/include/net/snmp.h 2013-09-12 13:26:29.208104037 -0500 > > @@ -126,7 +126,7 @@ struct linux_xfrm_mib { > > extern __typeof__(type) __percpu *name[SNMP_ARRAY_SZ] > > > > #define SNMP_INC_STATS_BH(mib, field) \ > > - __this_cpu_inc(mib[0]->mibs[field]) > > + raw_cpu_inc(mib[0]->mibs[field]) > > > > #define SNMP_INC_STATS_USER(mib, field) \ > > this_cpu_inc(mib[0]->mibs[field]) > > @@ -141,7 +141,7 @@ struct linux_xfrm_mib { > > this_cpu_dec(mib[0]->mibs[field]) > > > > #define SNMP_ADD_STATS_BH(mib, field, addend) \ > > - __this_cpu_add(mib[0]->mibs[field], addend) > > + raw_cpu_add(mib[0]->mibs[field], addend) > > Are the networking folks fine with allowing unafe operations of SNMP stats > in preemptible sections, or should the kernel produce an optional warning > message if CONFIG_PREEMPT_DEBUG=y and these ops are used in preemptible > (non-bh, non-irq-handler, non-irqs-off, etc.) sections? > > RAW_SNMP_*_STATS() ops could be used to annotate those places where that > kind of usage is safe.
I would rather not use RAW_ prefix in the macro, but add debugging check to make sure we use _BH() variant in the right context.
BUG_ON(!in_softirq())
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