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Date: Thu, 14 Nov 2013 23:48:12 -0500 From: Steven Rostedt <rostedt@...dmis.org> To: LKML <linux-kernel@...r.kernel.org> Cc: Terje Bergstrom <tbergstrom@...dia.com>, Arto Merilainen <amerilainen@...dia.com>, Thierry Reding <thierry.reding@...onic-design.de>, Erik Faye-Lund <kusmabite@...il.com> Subject: Why have another variable deciding a tracepoint? I've been reviewing different users of tracepoints and I stumbled across this: drivers/gpu/host1x/cdma.c: host1x_cdma_push() if (host1x_debug_trace_cmdbuf) trace_host1x_cdma_push(dev_name(cdma_to_channel(cdma)->dev), op1, op2); That host1x_debug_trace_cmdbuf is a variable that gets set by another debugfs file "trace_cmdbuf" that is custom to this driver. Why? The tracepoint host1x_cdma_push is already controlled by either ftrace or perf. If it gets enabled by perf or ftrace, it still wont be traced unless we also enable this trace_cmdbuf. Is there some reason for this? I can't figure it out from the change log: 6236451d83a720 ("gpu: host1x: Add debug support"). As tracepoints uses jump labels, there is no branch cost associated with them. That is, they are either a direct jump, or a nop (in most cases a nop). But here you added the overhead of a conditional branch depending on this variable. If this is truly needed, then use TRACE_EVENT_CONDITION() for that tracepoint. /me is baffled -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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