On 05/05/2020 05:00 PM, Al Grant wrote:
The patch below does the kernel and userspace side but is not complete. The problem is that userspace perf creates the metadata copy of TRCCONFIGR based on its request (and fills in the other id registers by reading sysfs), but the detection of EL2/E2H happens in the kernel which adjusts TRCCONFIGR, and it's this config which is needed for decode. I
see three ways round this:
- have userspace test to see if the kernel is EL2 (somehow) and adjust
the metadata to mirror what the kernel is doing
- have the kernel pass the adjusted TRCCONFIGR back so perf can put it
in the metadata
- have the perf decoder get the thread id from whichever of VMID and
CONTEXTID is available in a PE_CONTEXT element
Obviously, the last is simplest, but it's a bodge, and means that OpenCSD will see VMIDs when its TRCCONFIGR says it won't. It's kind of cleanest to get the real TRCCONFIGR somehow, but how do we do that?
We do get TRCCONFIGR in the perf records. We should simply make sure we get the uptodate value (wherever we are getting it from).
The copy in PERF_RECORD_AUXINFO (which is a synthetic record created by userspace perf) is, I believe, as I said:
"userspace perf creates the metadata copy of TRCCONFIGR based on its request".
So if the kernel modifies it based on information only the kernel knows, there's no current way to get the actual value. That was what I was trying to address with my suggestions.
Have I missed some place the actual TRCCONFIGR is already being returned in other perf records?
The sysfs is one place where we could expose this and this could be then consumed by the perf tool while creating the TRCCONFIGR. Since the EL can't change, this could be a onetime probe activity.
Cheers Suzuki
Al
Al
diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c index a128b5063f46..96488a0cfdcf 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x.c +++ b/drivers/hwtracing/coresight/coresight-etm4x.c @@ -353,8 +353,32 @@ static int etm4_parse_event_config(struct
etmv4_drvdata *drvdata,
} if (attr->config & BIT(ETM_OPT_CTXTID))
/* bit[6], Context ID tracing bit */config->cfg |= BIT(ETM4_CFG_BIT_CTXTID);
{/** Enable context-id tracing. The assumption is that this* will work with CONFIG_PID_IN_CONTEXTIDR to trace process* id changes and support decode of multiple processes.* But ETM's context id trace traces physical CONTEXTIDR_EL1,* while the logical CONTEXTIDR_EL1 that is written to on* process switch is either physical CONTEXTIDR_EL1 or* CONTEXTIDR_EL2 depending on HCR_EL2.E2H. On principle* we should continue to use logical CONTEXTIDR_EL1.* In order to trace physical CONTEXTIDR_EL2, we need to* enable VMID tracing and use the VMIDOPT flag to trace* CONTEXTIDR_EL2 rather than VTTBR.VMID in the VMID field.* Trace decoders will need to inspect TRCCONFIGR and use* either the CID or the VMID field from the trace packet.*/if (!(is_kernel_in_hyp_mode() &&(read_sysreg(hcr_el2) & BIT(34)) != 0)) {The patch looks good to me. We should be careful about the register access, as we assume that the kernel is running in AArch64 mode above, which may not be necessarily true.
Suzuki