Messages in this thread | | | From | Andi Kleen <> | Subject | Re: [PATCH] perf/x86/intel/pt: Fix sampling using single range output | Date | Tue, 15 Nov 2022 11:46:32 -0800 |
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Peter Zijlstra <peterz@infradead.org> writes:
> On Mon, Nov 14, 2022 at 01:10:38PM +0200, Adrian Hunter wrote: >> On 14/11/22 12:51, Peter Zijlstra wrote: >> > On Sat, Nov 12, 2022 at 05:15:08PM +0200, Adrian Hunter wrote: >> >> Deal with errata TGL052, ADL037 and RPL017 "Trace May Contain Incorrect >> >> Data When Configured With Single Range Output Larger Than 4KB" by >> >> disabling single range output whenever larger than 4KB. >> >> >> >> Fixes: 670638477aed ("perf/x86/intel/pt: Opportunistically use single range output mode") >> >> Cc: stable@vger.kernel.org >> >> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com> >> >> --- >> >> arch/x86/events/intel/pt.c | 9 +++++++++ >> >> 1 file changed, 9 insertions(+) >> >> >> >> diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c >> >> index 82ef87e9a897..42a55794004a 100644 >> >> --- a/arch/x86/events/intel/pt.c >> >> +++ b/arch/x86/events/intel/pt.c >> >> @@ -1263,6 +1263,15 @@ static int pt_buffer_try_single(struct pt_buffer *buf, int nr_pages) >> >> if (1 << order != nr_pages) >> >> goto out; >> >> >> >> + /* >> >> + * Some processors cannot always support single range for more than >> >> + * 4KB - refer errata TGL052, ADL037 and RPL017. Future processors might >> >> + * also be affected, so for now rather than trying to keep track of >> >> + * which ones, just disable it for all. >> >> + */ >> >> + if (nr_pages > 1) >> >> + goto out; >> > >> > This effectively declares single-output-mode dead? Because I don't think >> > anybody uses PT with a single 4K buffer. >> >> 4K is the default size for "sample mode" i.e. stuffing 4KB of Intel PT trace >> data into a PERF_RECORD_SAMPLE record that has sample_type bit PERF_SAMPLE_AUX >> >> e.g. >> >> $ perf record -vv --aux-sample -e '{intel_pt//u,cycles:u}' uname 2>err.txt >> Linux >> $ grep aux_sample_size err.txt >> aux_sample_size 4096 > > Ah, ok. Not as bad then. Anyway, I'll go queue it for perf/urgent I > suppose.
It would be better to only limit on the CPUs with the bug because switching buffers causes some extra latencies. So this patch may regress PT overhead or tail latencies.
-Andi
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