On 11/05/2021 11:05, Leo Yan wrote:
On Mon, May 10, 2021 at 01:39:04PM +0800, Leo Yan wrote:
On Fri, May 07, 2021 at 01:02:35PM +0300, James Clark wrote:
On 07/05/2021 12:58, James Clark wrote:
There is an intermittent issue on Trogdor devices that results in all Coresight timestamps having a value of zero.
I've attached a file here that has the issue. From the dump you can see the zero timestamps:
Idx:69; ID:10; I_TIMESTAMP : Timestamp.; Updated val = 0x0 Idx:71; ID:10; I_ATOM_F1 : Atom format 1.; E Idx:72; ID:10; I_ADDR_S_IS0 : Address, Short, IS0.; Addr=0xFFFFFFE723C65824 ~[0x5824]This doesn't have an impact on decoding as they end up being decoded in file order as in with timeless mode.
Just remind, as Mike has mentioned that if the timestamp is zero, it means the hardware setting for timestamp is not enabled properly. So for system wide or per CPU mode tracing, it's better to double check what's the reason the timestamp is not enabled properly.
IIUC, this patch breaks the existed rational in the code. Let's think about there have 4 CPUs, every CPU has its own AUX trace buffer, and when decode the trace data, it will use 4 queues to track the packets and every queue has its timestamp.
CPU0: cs_etm_queue -> ... -> packet_queue->timestamp CPU1: cs_etm_queue -> ... -> packet_queue->timestamp CPU2: cs_etm_queue -> ... -> packet_queue->timestamp CPU3: cs_etm_queue -> ... -> packet_queue->timestamp
The issue is if all CPUs' timestamp are zero, it's impossible to find a way to synthesize samples in the right time order.
I saw Denis's replying for the hardware issue for timestamp, wander if can add a new option "--force-aux-ts-zero" to override the hardware timestamp issue. Without the option "--force-aux-ts-zero", the developers still have chance to observe the failure case caused by the abnormal timestamps.
Hi Leo,
Now that you mention arguments, I remembered that you already can force something like that with --disable-order.
There is also a recent commit "perf intel-pt: Support Z itrace option for timeless decoding" which introduces this option:
@@ -869,6 +869,7 @@ The letters are: L synthesize last branch entries on existing event records s skip initial number of events q quicker (less detailed) decoding + Z prefer to ignore timestamps (so-called "timeless" decoding)
I will investigate if these are more relevant to fix this issue.
Thanks James
Thanks, Leo