From: Peter Zijlstra <peterz@infradead.org>
To: Hugh Dickins <hughd@google.com>
Cc: "Metzger, Markus T" <markus.t.metzger@intel.com>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
"Shishkin, Alexander" <alexander.shishkin@intel.com>,
"Kleen, Andi" <andi.kleen@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Stephane Eranian <eranian@google.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [bug] kpti, perf_event, bts: sporadic truncated trace
Date: Fri, 13 Jul 2018 12:53:16 +0200 [thread overview]
Message-ID: <20180713105316.GX2494@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <alpine.LSU.2.11.1807121743050.5425@eggly.anvils>
On Thu, Jul 12, 2018 at 06:22:13PM -0700, Hugh Dickins wrote:
> A little "optimization" crept into alloc_bts_buffer() along the way,
> which now places bts_interrupt_threshold not on a record boundary.
> And Stephane has shown me the sentence in Vol 3B, 17.4.9, which says
> "This address must point to an offset from the BTS buffer base that
> is a multiple of the BTS record size."
>
> Please give the patch below a try, and let us know if it helps (if it
> does not, then I think we'll need perfier expertise than I can give).
Ooh, good find!
> --- 4.18-rc4/arch/x86/events/intel/ds.c 2018-06-03 14:15:21.000000000 -0700
> +++ linux/arch/x86/events/intel/ds.c 2018-07-12 17:38:28.471378616 -0700
> @@ -408,9 +408,11 @@ static int alloc_bts_buffer(int cpu)
> ds->bts_buffer_base = (unsigned long) cea;
> ds_update_cea(cea, buffer, BTS_BUFFER_SIZE, PAGE_KERNEL);
> ds->bts_index = ds->bts_buffer_base;
> - max = BTS_RECORD_SIZE * (BTS_BUFFER_SIZE / BTS_RECORD_SIZE);
> - ds->bts_absolute_maximum = ds->bts_buffer_base + max;
> - ds->bts_interrupt_threshold = ds->bts_absolute_maximum - (max / 16);
> + max = BTS_BUFFER_SIZE / BTS_RECORD_SIZE;
> + ds->bts_absolute_maximum = ds->bts_buffer_base +
> + max * BTS_RECORD_SIZE;
> + ds->bts_interrupt_threshold = ds->bts_absolute_maximum -
> + (max / 16) * BTS_RECORD_SIZE;
> return 0;
> }
>
prev parent reply other threads:[~2018-07-13 10:53 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-12 10:15 [bug] kpti, perf_event, bts: sporadic truncated trace Metzger, Markus T
2018-07-12 14:01 ` Andi Kleen
2018-07-13 1:22 ` Hugh Dickins
2018-07-13 10:06 ` Metzger, Markus T
2018-07-13 18:31 ` Hugh Dickins
2018-07-13 10:53 ` Peter Zijlstra [this message]
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