Messages in this thread | | | Date | Mon, 14 Nov 2022 13:59:28 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] perf/x86/intel/pt: Fix sampling using single range output |
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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.
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