* [PATCH v2] perf/x86/intel: Add support for MISPREDICT bit on Knights Landing cpus
@ 2018-07-30 14:28 Jacek Tomaka
2018-07-30 16:17 ` Peter Zijlstra
0 siblings, 1 reply; 3+ messages in thread
From: Jacek Tomaka @ 2018-07-30 14:28 UTC (permalink / raw)
To: peterz, linux-kernel, mingo, tglx; +Cc: Jacek Tomaka
From: Jacek Tomaka <jacek.tomaka@poczta.fm>
Problem: perf did not show branch predicted/mispredicted bit in brstack.
Output of perf -F brstack for profile collected
Before:
0x4fdbcd/0x4fdc03/-/-/-/0
0x45f4c1/0x4fdba0/-/-/-/0
0x45f544/0x45f4bb/-/-/-/0
0x45f555/0x45f53c/-/-/-/0
0x7f66901cc24b/0x45f555/-/-/-/0
0x7f66901cc22e/0x7f66901cc23d/-/-/-/0
0x7f66901cc1ff/0x7f66901cc20f/-/-/-/0
0x7f66901cc1e8/0x7f66901cc1fc/-/-/-/0
After:
0x4fdbcd/0x4fdc03/P/-/-/0
0x45f4c1/0x4fdba0/P/-/-/0
0x45f544/0x45f4bb/P/-/-/0
0x45f555/0x45f53c/P/-/-/0
0x7f66901cc24b/0x45f555/P/-/-/0
0x7f66901cc22e/0x7f66901cc23d/P/-/-/0
0x7f66901cc1ff/0x7f66901cc20f/P/-/-/0
0x7f66901cc1e8/0x7f66901cc1fc/P/-/-/0
Cause:
As mentioned in Software Development Manual vol 3, 17.4.8.1,
IA32_PERF_CAPABILITIES[5:0] indicates the format of the address that is
stored in the LBR stack. Knights Landing reports 1 (LBR_FORMAT_LIP) as
its format. Despite that, registers containing FROM address of the branch,
do have MISPREDICT bit but because of the format indicated in
IA32_PERF_CAPABILITIES[5:0], LBR did not read MISPREDICT bit.
Solution:
Teach LBR about above Knights Landing quirk and make it read MISPREDICT bit.
---
arch/x86/events/intel/lbr.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
index cf372b9055..043aa09f3a 100644
--- a/arch/x86/events/intel/lbr.c
+++ b/arch/x86/events/intel/lbr.c
@@ -19,7 +19,7 @@ enum {
LBR_FORMAT_MAX_KNOWN = LBR_FORMAT_TIME,
};
-static const enum {
+static enum {
LBR_EIP_FLAGS = 1,
LBR_TSX = 2,
} lbr_desc[LBR_FORMAT_MAX_KNOWN + 1] = {
@@ -1230,4 +1230,8 @@ void intel_pmu_lbr_init_knl(void)
x86_pmu.lbr_sel_mask = LBR_SEL_MASK;
x86_pmu.lbr_sel_map = snb_lbr_sel_map;
+
+ /* Knights Landing does have MISPREDICT bit */
+ if (x86_pmu.intel_cap.lbr_format == LBR_FORMAT_LIP)
+ lbr_desc[LBR_FORMAT_LIP] |= LBR_EIP_FLAGS;
}
--
2.17.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2] perf/x86/intel: Add support for MISPREDICT bit on Knights Landing cpus
2018-07-30 14:28 [PATCH v2] perf/x86/intel: Add support for MISPREDICT bit on Knights Landing cpus Jacek Tomaka
@ 2018-07-30 16:17 ` Peter Zijlstra
[not found] ` <CAKVxXCVjBaW1kFA48r-bKwrnzR9+SaFXtgaBTb-tr6QHeu1srg@mail.gmail.com>
0 siblings, 1 reply; 3+ messages in thread
From: Peter Zijlstra @ 2018-07-30 16:17 UTC (permalink / raw)
To: Jacek Tomaka; +Cc: linux-kernel, mingo, tglx, Jacek Tomaka
On Mon, Jul 30, 2018 at 10:28:13PM +0800, Jacek Tomaka wrote:
> From: Jacek Tomaka <jacek.tomaka@poczta.fm>
>
> Problem: perf did not show branch predicted/mispredicted bit in brstack.
>
> Output of perf -F brstack for profile collected
>
> Before:
> 0x4fdbcd/0x4fdc03/-/-/-/0
> 0x45f4c1/0x4fdba0/-/-/-/0
> 0x45f544/0x45f4bb/-/-/-/0
> 0x45f555/0x45f53c/-/-/-/0
> 0x7f66901cc24b/0x45f555/-/-/-/0
> 0x7f66901cc22e/0x7f66901cc23d/-/-/-/0
> 0x7f66901cc1ff/0x7f66901cc20f/-/-/-/0
> 0x7f66901cc1e8/0x7f66901cc1fc/-/-/-/0
>
> After:
> 0x4fdbcd/0x4fdc03/P/-/-/0
> 0x45f4c1/0x4fdba0/P/-/-/0
> 0x45f544/0x45f4bb/P/-/-/0
> 0x45f555/0x45f53c/P/-/-/0
> 0x7f66901cc24b/0x45f555/P/-/-/0
> 0x7f66901cc22e/0x7f66901cc23d/P/-/-/0
> 0x7f66901cc1ff/0x7f66901cc20f/P/-/-/0
> 0x7f66901cc1e8/0x7f66901cc1fc/P/-/-/0
>
> Cause:
> As mentioned in Software Development Manual vol 3, 17.4.8.1,
> IA32_PERF_CAPABILITIES[5:0] indicates the format of the address that is
> stored in the LBR stack. Knights Landing reports 1 (LBR_FORMAT_LIP) as
> its format. Despite that, registers containing FROM address of the branch,
> do have MISPREDICT bit but because of the format indicated in
> IA32_PERF_CAPABILITIES[5:0], LBR did not read MISPREDICT bit.
>
> Solution:
> Teach LBR about above Knights Landing quirk and make it read MISPREDICT bit.
> ---
> arch/x86/events/intel/lbr.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
> index cf372b9055..043aa09f3a 100644
> --- a/arch/x86/events/intel/lbr.c
> +++ b/arch/x86/events/intel/lbr.c
> @@ -19,7 +19,7 @@ enum {
> LBR_FORMAT_MAX_KNOWN = LBR_FORMAT_TIME,
> };
>
> -static const enum {
> +static enum {
> LBR_EIP_FLAGS = 1,
> LBR_TSX = 2,
> } lbr_desc[LBR_FORMAT_MAX_KNOWN + 1] = {
> @@ -1230,4 +1230,8 @@ void intel_pmu_lbr_init_knl(void)
>
> x86_pmu.lbr_sel_mask = LBR_SEL_MASK;
> x86_pmu.lbr_sel_map = snb_lbr_sel_map;
> +
> + /* Knights Landing does have MISPREDICT bit */
> + if (x86_pmu.intel_cap.lbr_format == LBR_FORMAT_LIP)
> + lbr_desc[LBR_FORMAT_LIP] |= LBR_EIP_FLAGS;
> }
So why not set lbr_format to LBR_FORMAT_EIP_FLAGS ?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] perf/x86/intel: Add support for MISPREDICT bit on Knights Landing cpus
[not found] ` <CAKVxXCVoRb8Hf18AmUF7RcyNy7JACKByj2FsVOSiO31=ZHFHYQ@mail.gmail.com>
@ 2018-07-30 16:48 ` Peter Zijlstra
0 siblings, 0 replies; 3+ messages in thread
From: Peter Zijlstra @ 2018-07-30 16:48 UTC (permalink / raw)
To: Jacek Tomaka; +Cc: linux-kernel, Ingo Molnar, Thomas Gleixner, Jacek Tomaka
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?On Tue, Jul 31, 2018 at 12:34:02AM +0800, Jacek Tomaka wrote:
> Ah, right:
> /*
> * Due to lack of segmentation in Linux the effective address (offset)
> * is the same as the linear address, allowing us to merge the LIP and EIP
> * LBR formats.
> */
>
> Yeah, LBR_FORMAT_EIP_FLAGS is ok as well. Would it be preffered?
Yeah, think so, that keeps the lookup table const.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2018-07-30 14:28 [PATCH v2] perf/x86/intel: Add support for MISPREDICT bit on Knights Landing cpus Jacek Tomaka
2018-07-30 16:17 ` Peter Zijlstra
[not found] ` <CAKVxXCVjBaW1kFA48r-bKwrnzR9+SaFXtgaBTb-tr6QHeu1srg@mail.gmail.com>
[not found] ` <CAKVxXCVoRb8Hf18AmUF7RcyNy7JACKByj2FsVOSiO31=ZHFHYQ@mail.gmail.com>
2018-07-30 16:48 ` Peter Zijlstra
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