On 5/17/2021 1:39 AM, Peter Zijlstra wrote:
On Tue, May 11, 2021 at 10:42:05AM +0800, Like Xu wrote:
+ if (pebs) {
+ /*
+ * The non-zero precision level of guest event makes the ordinary
+ * guest event becomes a guest PEBS event and triggers the host
+ * PEBS PMI handler to determine whether the PEBS overflow PMI
+ * comes from the host counters or the guest.
+ *
+ * For most PEBS hardware events, the difference in the software
+ * precision levels of guest and host PEBS events will not affect
+ * the accuracy of the PEBS profiling result, because the "event IP"
+ * in the PEBS record is calibrated on the guest side.
+ */
+ attr.precise_ip = 1;
+ }
You've just destroyed precdist, no?
precdist can mean multiple things:
- Convert cycles to the precise INST_RETIRED event. That is not
meaningful for virtualization because "cycles" doesn't exist, just the
raw events.
- For GLC+ and TNT+ it will force the event to a specific counter that
is more precise. This would be indeed "destroyed", but right now the
patch kit only supports Icelake which doesn't support that anyways.
So I think the code is correct for now, but will need to be changed for
later CPUs. Should perhaps fix the comment though to discuss this.
-Andi
