On Thu, Feb 19, 2015 at 06:57:24PM +0100, Paolo Bonzini wrote:
>
>
> On 19/02/2015 18:55, Andrew Jones wrote:
> >> > > (I don't have an exact number for how many times it went to EL1 because
> >> > > access_mair() doesn't have a trace point.)
> >> > > (I got the 62873 number by testing a 3rd kernel build that only had patch
> >> > > 3/3 applied to the base, and counting kvm_toggle_cache events.)
> >> > > (The number 50 is the number of kvm_toggle_cache events *without* 3/3
> >> > > applied.)
> >> > >
> >> > > I consider this bad news because, even considering it only goes to EL2,
> >> > > it goes a ton more than it used to. I realize patch 3/3 isn't the final
> >> > > plan for enabling traps though.
>
> If a full guest boots, can you try timing a kernel compile?
>
Guests boot. I used an 8 vcpu, 14G memory guest; compiled the kernel 4
times inside the guest for each host kernel; base and mair. I dropped
the time from the first run of each set, and captured the other 3.
Command line used below. Time is from the
Elapsed (wall clock) time (h:mm:ss or m:ss):
output of /usr/bin/time - the host's wall clock.
/usr/bin/time --verbose ssh $VM 'cd kernel && make -s clean && make -s -j8'
Results:
base: 3:06.11 3:07.00 3:10.93
mair: 3:08.47 3:06.75 3:04.76
So looks like the 3 orders of magnitude greater number of traps
(only to el2) don't impact kernel compiles.
Then I thought I'd be able to quick measure the number of cycles
a trap to el2 takes with this kvm-unit-tests test
int main(void)
{
unsigned long start, end;
unsigned int sctlr;
asm volatile(
" mrs %0, sctlr_el1\n"
" msr pmcr_el0, %1\n"
: "=&r" (sctlr) : "r" (5));
asm volatile(
" mrs %0, pmccntr_el0\n"
" msr sctlr_el1, %2\n"
" mrs %1, pmccntr_el0\n"
: "=&r" (start), "=&r" (end) : "r" (sctlr));
printf("%llx\n", end - start);
return 0;
}
after applying this patch to kvm
diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
index bb91b6fc63861..5de39d740aa58 100644
--- a/arch/arm64/kvm/hyp.S
+++ b/arch/arm64/kvm/hyp.S
@@ -770,7 +770,7 @@
mrs x2, mdcr_el2
and x2, x2, #MDCR_EL2_HPMN_MASK
- orr x2, x2, #(MDCR_EL2_TPM | MDCR_EL2_TPMCR)
+// orr x2, x2, #(MDCR_EL2_TPM | MDCR_EL2_TPMCR)
orr x2, x2, #(MDCR_EL2_TDRA | MDCR_EL2_TDOSA)
// Check for KVM_ARM64_DEBUG_DIRTY, and set debug to trap
But I get zero for the cycle count. Not sure what I'm missing.
drew
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