lkml.org 
[lkml]   [2021]   [Oct]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
SubjectRe: [RFCv1 4/4] perf: arm_spe: Dynamically switch PID tracing to contextidr
From
Date


On 21/10/2021 14:45, Leo Yan wrote:
> Now Arm64 provides API for enabling and disable PID tracing, Arm SPE
> driver invokes these functions to dynamically enable it during
> profiling when the program runs in root PID name space, and disable PID
> tracing when the perf event is stopped.
>
> Device drivers should not depend on CONFIG_PID_IN_CONTEXTIDR for PID
> tracing, so this patch uses the consistent condition for setting bit
> EL1_CX for PMSCR.

Hi Leo,

I've been testing this change, but I'm seeing something strange. Not sure
if it's a problem on my side or not yet. With this command:

sudo ./perf record -vvv -e arm_spe//u -- taskset --cpu-list 1 bash -c ls

I'm only seeing 0 values for context:

sudo ./perf report -D | grep CONTEXT

. 00038dce: 65 00 00 00 00 CONTEXT 0x0 el2
. 00038e0e: 65 00 00 00 00 CONTEXT 0x0 el2

I added a printk to the function, and I see it print non zero values, although
there are some zero ones mixed in there too:

diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index 0c1669db19a1..8f0fb43a5fac 100644
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -33,7 +33,8 @@ static inline void contextidr_thread_switch(struct task_struct *next)
if (!static_branch_unlikely(&contextidr_in_use))
return;

- write_sysreg(task_pid_nr(next), contextidr_el1);
+ printk("Set %d\n", task_pid_nr(next));
+ write_sysreg(task_pid_nr(next), contextidr_el2);
isb();
}

Results in this:

[ 53.257905] Set 77
[ 53.257909] Set 0
[ 53.258180] Set 77
[ 53.258183] Set 0
[ 53.258385] Set 309
[ 53.258385] Set 172
[ 53.258425] Set 77
[ 53.258443] Set 990
[ 53.258449] Set 77
[ 53.258455] Set 990
[ 53.258467] Set 310
[ 53.258719] Set 7
[ 53.258728] Set 77
[ 53.258731] Set 0
[ 53.258733] Set 0
[ 53.258738] Set 7


Without your patchset I don't get 0 values in the SPE trace anymore:

. 0000050e: 65 b1 01 00 00 CONTEXT 0x1b1 el2
. 0000054e: 65 b1 01 00 00 CONTEXT 0x1b1 el2
. 0000058e: 65 ac 01 00 00 CONTEXT 0x1ac el2
. 000005ce: 65 ac 01 00 00 CONTEXT 0x1ac el2
\
 
 \ /
  Last update: 2021-10-22 17:37    [W:0.386 / U:0.500 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site