Messages in this thread | | | Date | Thu, 27 Nov 2008 14:30:31 +0100 | From | "stephane eranian" <> | Subject | Re: [patch 05/24] perfmon: X86 generic code (x86) |
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On Thu, Nov 27, 2008 at 1:45 PM, Andi Kleen <andi@firstfloor.org> wrote: >> What if a threads reprograms the counters while another is reading them? > > In the worst case you get an invalid event, which is then discarded. > I think. I've never tried to understand it in all details, but > at least it seems to work. > >> How is the buffer reset? > > drivers/oprofile/cpu_buffer.c: > > /* Resets the cpu buffer to a sane state. */ > void cpu_buffer_reset(struct oprofile_cpu_buffer *cpu_buf) > { > /* reset these to invalid values; the next sample > * collected will populate the buffer with proper > * values to initialize the buffer > */ > cpu_buf->last_is_kernel = -1; > cpu_buf->last_task = NULL; > } > What about a thread doing this and another one in the middle of read the buffer?
Or what about a thread trying to reset the buffer while you're processing an PMU interrupt on another CPU. I know each buffer is per-CPU, but that does not prevent two threads for trying to operate on it at the same time from different CPUs.
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