Messages in this thread | | | Date | Tue, 24 Sep 2013 09:32:50 +0200 | From | Ingo Molnar <> | Subject | Re: [pchecks v1 2/4] Use raw cpu ops for calls that would trigger with checks |
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(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.
Thanks,
Ingo
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