Messages in this thread | | | Subject | Re: [PATCH 5/5] irqtime: drop local_irq_save/restore from irqtime_account_irq | From | Rik van Riel <> | Date | Thu, 23 Jun 2016 11:24:13 -0400 |
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On Thu, 2016-06-23 at 15:52 +0200, Paolo Bonzini wrote: > > On 22/06/2016 23:55, Rik van Riel wrote: > > > > > > > > > > > > > + hardirq_time = > > > > READ_ONCE(per_cpu(cpu_hardirq_time, > > > > cpu)); > > > Which makes this per_cpu(,cpu) usage somewhat curious. What's > > > wrong > > > with __this_cpu_read() ? > > I played around with it a bit, and it seems that > > __this_cpu_read does not want to nest inside > > READ_ONCE. Nobody else seems to be doing that, > > either. > According to arch/x86/include/asm/percpu.h, this_cpu_read always has > READ_ONCE semantics, but I cannot find that in include/asm-generic > /percpu.h. It probably just works because of all the layers of goo, > but > something like this (101% untested) would make me feel safer: > Are READ_ONCE semantics desired for every per-cpu read?
> > Back to READ_ONCE(per_cpu(,cpu)) it is... > What about READ_ONCE(this_cpu_ptr())?
I tried that yesterday, because it looked like it would work. Unfortunately, it does not.
CC kernel/sched/cputime.o kernel/sched/cputime.c: In function ‘irqtime_account_irq’: kernel/sched/cputime.c:107:71: warning: initialization makes pointer from integer without a cast [-Wint-conversion] kernel/sched/cputime.c:107:298: error: invalid type argument of unary ‘*’ (have ‘u64 {aka long long unsigned int}’) kernel/sched/cputime.c:107:428: warning: initialization makes pointer from integer without a cast [-Wint-conversion] kernel/sched/cputime.c:107:655: error: invalid type argument of unary ‘*’ (have ‘u64 {aka long long unsigned int}’) kernel/sched/cputime.c:107:749: warning: initialization makes pointer from integer without a cast [-Wint-conversion] kernel/sched/cputime.c:107:976: error: invalid type argument of unary ‘*’ (have ‘u64 {aka long long unsigned int}’) kernel/sched/cputime.c:107:1087: warning: initialization makes pointer from integer without a cast [-Wint-conversion] kernel/sched/cputime.c:107:1314: error: invalid type argument of unary ‘*’ (have ‘u64 {aka long long unsigned int}’) kernel/sched/cputime.c:107:1408: warning: initialization makes pointer from integer without a cast [-Wint-conversion] kernel/sched/cputime.c:107:1635: error: invalid type argument of unary ‘*’ (have ‘u64 {aka long long unsigned int}’) kernel/sched/cputime.c: In function ‘irqtime_account_hi_update’: kernel/sched/cputime.c:145:175: warning: comparison of distinct pointer types lacks a cast kernel/sched/cputime.c: In function ‘irqtime_account_si_update’: kernel/sched/cputime.c:162:182: warning: comparison of distinct pointer types lacks a cast scripts/Makefile.build:291: recipe for target 'kernel/sched/cputime.o' failed make[1]: *** [kernel/sched/cputime.o] Error 1 Makefile:1594: recipe for target 'kernel/sched/' failed make: *** [kernel/sched/] Error 2
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