On Wed, 24 Mar 2021 15:04:16 +0200
"Tzvetomir Stoyanov (VMware)" <tz.stoyanov@xxxxxxxxx> wrote:
> In host-guest tracing session, all peers should use the same tracing
> clock. If there is no user configured trace clock, the current logic
> assumes "local" clock for the session. This could be wrong, as other
> clock than "local" could be already configured on the host, before
> running trace-cmd. The default clock for host-guest tracing session
> should be rertieved from the host's "trace_clock" file.
Actually this is wrong. If clock is not specified, you should check the
first instance, because if the user does:
# trace-cmd start -B foo -p nop -C myclock
# trace-cmd record -B foo -e kvm -e sched -A Guest -e all
It should not use the clock from the top instance, but instead the first
instance.
I'm trying to make sure tha trace-cmd does not affect or even use the top
instance if it is not part of the command line.
>
> Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@xxxxxxxxx>
> ---
> tracecmd/trace-record.c | 40 ++++++++++++++++++++++++++++++----------
> 1 file changed, 30 insertions(+), 10 deletions(-)
>
> diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
> index f90fdbe4..2fc6723a 100644
> --- a/tracecmd/trace-record.c
> +++ b/tracecmd/trace-record.c
> @@ -6455,11 +6455,12 @@ static void get_tsc_offset(struct common_record_context *ctx)
>
> static void set_tsync_params(struct common_record_context *ctx)
> {
> - const char *clock = ctx->clock;
> struct buffer_instance *instance;
> int shift, mult;
> bool force_tsc = false;
> + char *clock = NULL;
>
> + if (!ctx->clock) {
> /*
> * If no clock is configured &&
> * KVM time sync protocol is available &&
> @@ -6468,18 +6469,35 @@ static void set_tsync_params(struct common_record_context *ctx)
> * force using the x86-tsc clock for this host-guest tracing session
> * and store TSC to nsec multiplier and shift.
> */
> - if (!clock && tsync_proto_is_supported("kvm") &&
> - clock_is_supported(NULL, TSC_CLOCK) &&
> - !get_tsc_nsec(&shift, &mult) && mult) {
> - clock = TSC_CLOCK;
> - ctx->tsc2nsec.mult = mult;
> - ctx->tsc2nsec.shift = shift;
> - ctx->tsc2nsec.offset = get_clock_now(TSC_CLOCK);
> - force_tsc = true;
> + if (tsync_proto_is_supported("kvm") &&
> + clock_is_supported(NULL, TSC_CLOCK) &&
So we want to test the first instance, not the top one.
-- Steve
> + !get_tsc_nsec(&shift, &mult) && mult) {
> + clock = strdup(TSC_CLOCK);
> + if (!clock)
> + die("Cannot not allocate clock");
> + ctx->tsc2nsec.mult = mult;
> + ctx->tsc2nsec.shift = shift;
> + ctx->tsc2nsec.offset = get_clock_now(TSC_CLOCK);
> + force_tsc = true;
> + } else {
> + /*
> + * Else, use the current clock of the first host instance
> + */
> + for_all_instances(instance) {
> + if (is_guest(instance))
> + continue;
> + clock = tracefs_get_clock(instance->tracefs);
> + break;
> + }
> + }
> + } else {
> + clock = strdup(ctx->clock);
> + if (!clock)
> + die("Cannot not allocate clock");
> }
>
> if (!clock && !ctx->tsync_loop_interval)
> - return;
> + goto out;
> for_all_instances(instance) {
> if (clock && !(instance->flags & BUFFER_FL_HAS_CLOCK)) {
> /* use the same clock in all tracing peers */
> @@ -6501,6 +6519,8 @@ static void set_tsync_params(struct common_record_context *ctx)
> }
> instance->tsync_loop_interval = ctx->tsync_loop_interval;
> }
> +out:
> + free(clock);
> }
>
> /*
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