On 9/12/2021 11:52 am, Jim Mattson wrote:
On Mon, Nov 29, 2021 at 11:42 PM Like Xu <like.xu.linux@xxxxxxxxx> wrote:
From: Like Xu <likexu@xxxxxxxxxxx>
The find_arch_event() returns a "unsigned int" value,
which is used by the pmc_reprogram_counter() to
program a PERF_TYPE_HARDWARE type perf_event.
The returned value is actually the kernel defined generic
Typo: generic.
perf_hw_id, let's rename it to pmc_perf_hw_id() with simpler
incoming parameters for better self-explanation.
Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
---
arch/x86/kvm/pmu.c | 8 +-------
arch/x86/kvm/pmu.h | 3 +--
arch/x86/kvm/svm/pmu.c | 8 ++++----
arch/x86/kvm/vmx/pmu_intel.c | 9 +++++----
4 files changed, 11 insertions(+), 17 deletions(-)
diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 09873f6488f7..3b3ccf5b1106 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -174,7 +174,6 @@ static bool pmc_resume_counter(struct kvm_pmc *pmc)
void reprogram_gp_counter(struct kvm_pmc *pmc, u64 eventsel)
{
unsigned config, type = PERF_TYPE_RAW;
- u8 event_select, unit_mask;
struct kvm *kvm = pmc->vcpu->kvm;
struct kvm_pmu_event_filter *filter;
int i;
@@ -206,17 +205,12 @@ void reprogram_gp_counter(struct kvm_pmc *pmc, u64 eventsel)
if (!allow_event)
return;
- event_select = eventsel & ARCH_PERFMON_EVENTSEL_EVENT;
- unit_mask = (eventsel & ARCH_PERFMON_EVENTSEL_UMASK) >> 8;
-
if (!(eventsel & (ARCH_PERFMON_EVENTSEL_EDGE |
ARCH_PERFMON_EVENTSEL_INV |
ARCH_PERFMON_EVENTSEL_CMASK |
HSW_IN_TX |
HSW_IN_TX_CHECKPOINTED))) {
The mechanics of the change look fine, but I do have some questions,
for my own understanding.
Why don't we just use PERF_TYPE_RAW for guest counters all of the
time? What is the advantage of matching entries in a table so that we
can use PERF_TYPE_HARDWARE?
The first reason is we need PERF_TYPE_HARDWARE for fixed counters.
And then we might wonder whether we can create perf-event faster
using PERF_TYPE_HARDWARE compared to PERF_TYPE_HARDWARE.
But the (current) answer is no, and probably the opposite:
# The cost (nanosecond) of calling perf_event_create_kernel_counter()
PERF_TYPE_RAW
Max= 1072211
Min= 11122
Avg= 41681.7
PERF_TYPE_HARDWARE
Max= 46184215
Min= 16194
Avg= 250650
So why don't we just use PERF_TYPE_RAW for just all gp counters ?
Hi Peter, do you have any comments to invalidate this proposal ?
Why do the HSW_IN_TX* bits result in bypassing this clause, when these
bits are extracted as arguments to pmc_reprogram_counter below?
Once upon the time, the "PERF_TYPE_RAW" was introduced in the
perf with comment "available TYPE space, raw is the max value",
which means, per my understanding, it's our final type choice
for creating a valid perf_event when HSW_IN_TX* bits are set
and KVM needs to hack other perf_event_attr stuff for this
HSW_IN_TX feature with the help of extracted arguments.
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>
