Messages in this thread | | | Date | Mon, 13 Sep 2010 17:13:34 +0200 | Subject | Re: [PATCH] perf_events: improve DS/BTS/PEBS buffer allocation | From | Stephane Eranian <> |
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On Mon, Sep 13, 2010 at 5:09 PM, Frederic Weisbecker <fweisbec@gmail.com> wrote: > On Mon, Sep 13, 2010 at 04:55:01PM +0200, Stephane Eranian wrote: >> The DS, BTS, and PEBS memory regions were allocated using kzalloc(), i.e., >> requesting contiguous physical memory. There is no such restriction on >> DS, PEBS and BTS buffers. Using kzalloc() could lead to error in case >> no contiguous physical memory is available. BTS is requesting 64KB, >> thus it can cause issues. PEBS is currently only requesting one page. >> Both PEBS and BTS are static buffers allocated for each CPU at the >> first user. When the last user exists, the buffers are released. >> >> All buffers are only accessed on the CPU they are attached to. >> kzalloc() does not take into account NUMA, thus all allocations >> are taking place on the NUMA node where the perf_event_open() is >> made. >> >> This patch switches allocation to vmalloc_node() to use non-contiguous >> physical memory and to allocate on the NUMA node corresponding to each >> CPU. We switched DS and PEBS although they do not cause problems today, >> to, at least, make the allocation on the correct NUMA node. In the future, >> the PEBS buffer size may increase. DS may also grow bigger than a page. >> This patch eliminates the memory allocation imbalance. >> >> vmalloc_node() returns page-aligned addresses which do conform with the >> restriction on PEBS buffer as documented by Intel in Vol3a section 16.9.4.2. >> >> Signed-off-by: Stephane Eranian <eranian@google.com> >> -- > > > For now I think you can not do this. vmalloc'ed memory can't be safely > accessed from NMIs in x86 because that might fault. And faults from NMIs > are not supported. They cause very bad things: return from fault calls > iret which reenables NMI, so NMI can nest but in the meantime there is > only one NMI stack, so that gets quickly messed up. > What kind of faults are you talking about here? TLB faults?
But I don't want contiguous memory. This puts unnecessary pressure on the memory subsystem. I have seen failures on my system because it could not find 64KB of contiguous physical, but there was clearly more than 64kb of physical memory available. And I want NUMA local allocations as well.
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