Messages in this thread Patch in this message | | | Subject | Re: [RFCv1 4/4] perf: arm_spe: Dynamically switch PID tracing to contextidr | From | James Clark <> | Date | Fri, 22 Oct 2021 16:36:05 +0100 |
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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
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