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[arm] Use CNTVCT_EL0 as profiling timestamp

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The raw cycle counter at PMCCNTR_EL0 works in qemu but seems to always
read as zero on physical hardware (tested on Juno r1 and Cavium
ThunderX), even after ensuring that PMCR_EL0.E and PMCNTENSET_EL0.C
are both enabled.

Use CNTVCT_EL0 instead; this seems to count at a lower resolution
(tens of CPU cycles), but is usable for profiling.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2016-05-11 21:44:23 +01:00
parent 6164741f81
commit 601706688b
1 changed files with 1 additions and 3 deletions
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4
src/arch/arm64/include/bits/profile.h
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@@ -21,9 +21,7 @@ profile_timestamp ( void ) {
uint64_t cycles; uint64_t cycles;
/* Read cycle counter */ /* Read cycle counter */
__asm__ __volatile__ ( "msr PMCR_EL0, %1\n\t" __asm__ __volatile__ ( "mrs %0, CNTVCT_EL0\n\t" : "=r" ( cycles ) );
"mrs %0, PMCCNTR_EL0\n\t"
: "=r" ( cycles ) : "r" ( 1 ) );
return cycles; return cycles;
} }