| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <5b690fab-1dff-0249-c210-d302d96aa13f@arm.com>
Date: Tue, 9 Nov 2021 11:15:02 +0000
From: German Gomez <german.gomez@....com>
To: Leo Yan <leo.yan@...aro.org>
Cc: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
acme@...nel.org, John Garry <john.garry@...wei.com>,
Will Deacon <will@...nel.org>,
Mathieu Poirier <mathieu.poirier@...aro.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...hat.com>,
Namhyung Kim <namhyung@...nel.org>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/3] perf arm-spe: Support hardware-based PID tracing
Hi Leo,
Thanks for the review.
On 06/11/2021 14:57, Leo Yan wrote:
> Hi German,
>
> On Tue, Nov 02, 2021 at 06:07:39PM +0000, German Gomez wrote:
>> If Arm SPE traces contain CONTEXT packets with PID info, use these
>> values for tracking pid of samples. Otherwise fall back to using context
>> switch events and display a message warning the user of possible timing
>> inaccuracies [1].
>>
>> [1] https://lore.kernel.org/lkml/f877cfa6-9b25-6445-3806-ca44a4042eaf@arm.com/
> First of all, I'd like to clarify one thing:
>
> The pid/tid has been supported for 'per-thread' mode, the function
> arm_spe_process_timeless_queues() invokes arm_spe_set_pid_tid_cpu() to
> initialize 'speq->tid' and assign auxtrace_queue's tid to it.
Ack.
I forgot to validate per-thread mode and didn't realize it was using the
timeless flow.
>
> Thus, in this patch set we only need to consider support context packet
> for CPU wide tracing and system wide tracing. The following comments
> are heavily based on this assumption.
>
>> Signed-off-by: German Gomez <german.gomez@....com>
>> ---
>> tools/perf/util/arm-spe.c | 123 ++++++++++++++++++++++++++++----------
>> 1 file changed, 92 insertions(+), 31 deletions(-)
>>
>> diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
>> index 230bc7ab2..00a409469 100644
>> --- a/tools/perf/util/arm-spe.c
>> +++ b/tools/perf/util/arm-spe.c
>> @@ -71,6 +71,7 @@ struct arm_spe {
>> u64 kernel_start;
>>
>> unsigned long num_events;
>> + u8 use_ctx_pkt_for_pid;
>> };
>>
>> struct arm_spe_queue {
>> @@ -226,6 +227,44 @@ static inline u8 arm_spe_cpumode(struct arm_spe *spe, u64 ip)
>> PERF_RECORD_MISC_USER;
>> }
>>
>> +static void arm_spe_set_pid_tid_cpu(struct arm_spe *spe,
>> + struct auxtrace_queue *queue)
>> +{
>> + struct arm_spe_queue *speq = queue->priv;
>> + pid_t tid;
>> +
>> + tid = machine__get_current_tid(spe->machine, speq->cpu);
>> + if (tid != -1) {
>> + speq->tid = tid;
>> + thread__zput(speq->thread);
>> + } else
>> + speq->tid = queue->tid;
>> +
>> + if ((!speq->thread) && (speq->tid != -1)) {
>> + speq->thread = machine__find_thread(spe->machine, -1,
>> + speq->tid);
>> + }
>> +
>> + if (speq->thread) {
>> + speq->pid = speq->thread->pid_;
>> + if (queue->cpu == -1)
>> + speq->cpu = speq->thread->cpu;
>> + }
>> +}
>> +
>> +static int arm_spe_set_tid(struct arm_spe_queue *speq, pid_t tid)
>> +{
>> + struct arm_spe *spe = speq->spe;
>> + int err = machine__set_current_tid(spe->machine, speq->cpu, tid, tid);
>> +
>> + if (err)
>> + return err;
>> +
>> + arm_spe_set_pid_tid_cpu(spe, &spe->queues.queue_array[speq->queue_nr]);
>> +
>> + return 0;
>> +}
>> +
>> static void arm_spe_prep_sample(struct arm_spe *spe,
>> struct arm_spe_queue *speq,
>> union perf_event *event,
>> @@ -460,6 +499,13 @@ static int arm_spe_run_decoder(struct arm_spe_queue *speq, u64 *timestamp)
>> * can correlate samples between Arm SPE trace data and other
>> * perf events with correct time ordering.
>> */
>> +
>> + if (spe->use_ctx_pkt_for_pid) {
>> + ret = arm_spe_set_tid(speq, speq->decoder->record.context_id);
>> + if (ret)
>> + return ret;
>> + }
>> +
> If trace contains context packet, we can give it the priority. So at
> here we can always update tid based on the latest context_id from the
> context packet.
>
> And for 'per thread' mode, we should not set pid/tid for it. The
> reason is arm_spe_set_tid() will return error for 'per thread' mode,
> because the 'speq->cpu' is -1, so it cannot set tid/pid for CPU '-1'.
>
> And if we detect there have context packet is incoming, we should set
> the flag 'spe->use_ctx_pkt_for_pid' true.
>
> How about below code:
>
> /* Update pid/tid info */
> record = &speq->decoder->record;
> if (!spe->timeless_decoding && record->context_id != (u64)-1) {
> ret = arm_spe_set_tid(speq, record->context_id);
> if (ret)
> return ret;
>
> spe->use_ctx_pkt_for_pid = 1;
> }
Yeah it looks good. The patch defined the two method as strictly
mutually exclusive, but I prefer this way better which is also more in
line with the previous RFC. Thanks for the suggestion.
>> ret = arm_spe_sample(speq);
>> if (ret)
>> return ret;
>> @@ -586,31 +632,6 @@ static bool arm_spe__is_timeless_decoding(struct arm_spe *spe)
>> return timeless_decoding;
>> }
>>
>> -static void arm_spe_set_pid_tid_cpu(struct arm_spe *spe,
>> - struct auxtrace_queue *queue)
>> -{
>> - struct arm_spe_queue *speq = queue->priv;
>> - pid_t tid;
>> -
>> - tid = machine__get_current_tid(spe->machine, speq->cpu);
>> - if (tid != -1) {
>> - speq->tid = tid;
>> - thread__zput(speq->thread);
>> - } else
>> - speq->tid = queue->tid;
>> -
>> - if ((!speq->thread) && (speq->tid != -1)) {
>> - speq->thread = machine__find_thread(spe->machine, -1,
>> - speq->tid);
>> - }
>> -
>> - if (speq->thread) {
>> - speq->pid = speq->thread->pid_;
>> - if (queue->cpu == -1)
>> - speq->cpu = speq->thread->cpu;
>> - }
>> -}
>> -
>> static int arm_spe_process_queues(struct arm_spe *spe, u64 timestamp)
>> {
>> unsigned int queue_nr;
>> @@ -641,7 +662,13 @@ static int arm_spe_process_queues(struct arm_spe *spe, u64 timestamp)
>> ts = timestamp;
>> }
>>
>> - arm_spe_set_pid_tid_cpu(spe, queue);
>> + /*
>> + * Here we only consider PID tracking based on switch events.
>> + * For tracking based on CONTEXT packets, the pid is assigned in the function
>> + * arm_spe_run_decoder() in order to support timeless decoding.
>> + */
>> + if (!spe->use_ctx_pkt_for_pid)
>> + arm_spe_set_pid_tid_cpu(spe, queue);
> Yeah, this is right; if without context packet, we need to update thread
> context at this point.
>
> Could you refine the comment like something:
>
> "The switch events has set pid/tid in the machine's context, here we
> update the thread and pid/tid info for spe queue."
Ack.
>
>> ret = arm_spe_run_decoder(speq, &ts);
>> if (ret < 0) {
>> @@ -740,8 +767,9 @@ static int arm_spe_process_event(struct perf_session *session,
>> if (err)
>> return err;
>>
>> - if (event->header.type == PERF_RECORD_SWITCH_CPU_WIDE ||
>> - event->header.type == PERF_RECORD_SWITCH)
>> + if (!spe->use_ctx_pkt_for_pid &&
>> + (event->header.type == PERF_RECORD_SWITCH_CPU_WIDE ||
>> + event->header.type == PERF_RECORD_SWITCH))
>>
>> err = arm_spe_context_switch(spe, event, sample);
>> }
>>
>> @@ -805,10 +833,16 @@ static int arm_spe_flush(struct perf_session *session __maybe_unused,
>> return ret;
>>
>> if (spe->timeless_decoding)
>> - return arm_spe_process_timeless_queues(spe, -1,
>> + ret = arm_spe_process_timeless_queues(spe, -1,
>> MAX_TIMESTAMP - 1);
>> + else
>> + ret = arm_spe_process_queues(spe, MAX_TIMESTAMP);
>>
>> - return arm_spe_process_queues(spe, MAX_TIMESTAMP);
>> + if (!spe->use_ctx_pkt_for_pid)
>> + ui__warning("Arm SPE CONTEXT packets not found in the traces.\n\n"
>> + "Matching of TIDs to SPE events could be inaccurate.\n\n");
> I think we only need to report the warning for no timeless case and
> it's not necessary to change code for timeless decoding, thus the
> change could be:
>
> ret = arm_spe_process_queues(spe, MAX_TIMESTAMP);
> if (!spe->use_ctx_pkt_for_pid)
> ui__warning("Arm SPE CONTEXT packets not found in the traces.\n"
> "Matching of TIDs to SPE events could be inaccurate.\n");
Ack (I will also return early if ret != 0).
>
>> +
>> + return ret;
>> }
>>
>> static void arm_spe_free_queue(void *priv)
>> @@ -1056,6 +1090,22 @@ arm_spe_synth_events(struct arm_spe *spe, struct perf_session *session)
>> return 0;
>> }
>>
>> +static bool arm_spe_is_ctx_pkt_enabled(struct arm_spe *spe)
>> +{
>> + struct auxtrace_queues *queues = &spe->queues;
>> + unsigned int i;
>> +
>> + for (i = 0; i < queues->nr_queues; i++) {
>> + struct auxtrace_queue *queue = &spe->queues.queue_array[i];
>> + struct arm_spe_queue *speq = queue->priv;
>> +
>> + if (speq)
>> + return speq->decoder->record.context_id != (u64) -1;
>> + }
>> +
>> + return false;
>> +}
>> +
>> int arm_spe_process_auxtrace_info(union perf_event *event,
>> struct perf_session *session)
>> {
>> @@ -1131,9 +1181,20 @@ int arm_spe_process_auxtrace_info(union perf_event *event,
>> if (err)
>> goto err_free_queues;
>>
>> - if (spe->queues.populated)
>> + if (spe->queues.populated) {
>> spe->data_queued = true;
>>
>> + /*
>> + * Ensure the first record of every queue can be read in the function
>> + * arm_spe_is_ctx_pkt_enabled()
>> + */
>> + err = arm_spe__update_queues(spe);
>> + if (err)
>> + goto err_free_queues;
>> +
>> + spe->use_ctx_pkt_for_pid = arm_spe_is_ctx_pkt_enabled(spe);
> I don't think this change is needed.
>
> arm_spe__setup_queue() will start to decode and it returns back the
> first record; then function arm_spe_run_decoder() will check
> 'record->context_id', if detect 'context_id' is not '-1' it will set
> 'spe->use_ctx_pkt_for_pid' as true.
>
> So here we don't need to invoke arm_spe__update_queues(). And I have
> some concern that this might introduce other potential issue,
> especially the callback process_auxtrace_info() usually is only used
> for early initializatoin rather than trace data decoding.
Ack, with the above change in arm_spe_run_decoder, this is no longer
needed.
Thanks,
German
>
> Thanks,
> Leo
>
>> + }
>> +
>> return 0;
>>
>> err_free_queues:
>> --
>> 2.25.1
>>
Powered by blists - more mailing lists