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Message-ID: <20190412114200.6c1a8593@gandalf.local.home> Date: Fri, 12 Apr 2019 11:42:00 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Raul Rangel <rrangel@...omium.org> Cc: linux-trace-devel@...r.kernel.org, linux-mmc@...r.kernel.org, djkurtz@...omium.org, zwisler@...omium.org, linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com> Subject: Re: [PATCH v1 1/4] trace_events: Add trace_print_register to print register fields On Fri, 12 Apr 2019 09:30:36 -0600 Raul Rangel <rrangel@...omium.org> wrote: > Ah, I wasn't aware that the format was exposed via sysfs. That makes > sense why the macros are used. I was using xhci-trace as my reference > point which just calls arbitrary functions. > > cat /sys/kernel/debug/tracing/events/xhci-hcd/xhci_handle_event/format > print fmt: "%s: %s", > xhci_ring_type_string(REC->type), > xhci_decode_trb(REC->field0, REC->field1, REC->field2, REC->field3) > > I'm guessing calling out to a function is not the way the framework was > intended to be used. Does this mean that every TRB type in xhci_decode_trb > should be its own trace event so the printf format isn't hidden inside > the code? You can add plugins to handle this. See tools/lib/traceevent/plugin_*.c > > > > > How does perf or trace-cmd parse this? To add something like this, you > > need them to have the same output as what is displayed by the trace > > file otherwise NAK. > > So for the short term I can remove __print_register. The SDHCI tracing > doesn't use it, but instead calls out to a method that calls > trace_print_register directly. Or I could move trace_print_register > into the sdhci-trace module. For the short term yeah. And you can add a plugin to the libtraceevent to teach trace-cmd and perf how to parse it. See "tep_register_print_function()" > > cat /sys/kernel/debug/tracing/events/sdhci/sdhci_read/format > > print fmt: "%s: %#x [%s] => %#x: %s", > __get_str(name), > REC->reg, > __print_symbolic(REC->reg & ~3UL, {0x00, "DMA_ADDRESS"}, ...), > REC->val, > sdhci_decode_register( p, REC->reg, REC->val, REC->mask ) > > The format prints out the raw value, so using perf or trace-cmd > will still have value, you just won't get the pretty print. > > For the long term I could make event-parser handle __print_register. I'm > assuming it just needs to handle the additional case? > https://github.com/torvalds/linux/blob/master/tools/lib/traceevent/event-parse.c#L3040 > Yes, I'm fine with adding new generic functions that can parse the code properly to libtraceevent. Anything added to the trace_event code should have a corresponding routine added to libtraceevent. Just remember, that those *are* user API, and once made, they can not change. Thanks! -- Steve
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