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Date: Wed, 17 Nov 2010 09:33:21 -0600 From: Tom Zanussi <tzanussi@...il.com> To: Peter Zijlstra <peterz@...radead.org> Cc: Ingo Molnar <mingo@...e.hu>, Ted Ts'o <tytso@....edu>, Thomas Gleixner <tglx@...utronix.de>, LKML <linux-kernel@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, Steven Rostedt <rostedt@...dmis.org>, Arjan van de Ven <arjan@...radead.org>, Arnaldo Carvalho de Melo <acme@...hat.com>, Frederic Weisbecker <fweisbec@...il.com>, Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Li Zefan <lizf@...fujitsu.com>, Jason Baron <jbaron@...hat.com>, "David S. Miller" <davem@...emloft.net>, Christoph Hellwig <hch@....de>, Pekka Enberg <penberg@...nel.org>, Lai Jiangshan <laijs@...fujitsu.com>, Eric Dumazet <eric.dumazet@...il.com> Subject: Re: [ANNOUNCE] New utility: 'trace' On Wed, 2010-11-17 at 15:11 +0100, Peter Zijlstra wrote: > On Wed, 2010-11-17 at 15:00 +0100, Ingo Molnar wrote: > > > But yes, it is functional. > > > > I suspect that is what matters mostly - unless you think that it's impossible to > > have a sane implementation of it, if the users come. > > I'm not sure, I raised the point several times, and I think Steve and > Tom though it was possible to implement sanely, but I'm not sure if it > was expression invariant (the fix that is). > > It would be very good to have a definite answer on that. > > The idea was to not let the filter engine work on the trace data (once > its gathered) but on the trace argument right at the beginning of the > tracepoint callchain, since some of the trace data is an expression of > the trace argument (say next->prio instead of next), the trace > expression wouldn't stay invariant, you'd have to write a different > filter for the same effect. > IIRC, I think the conclusion we came to was that it could be done mechanically if for example the right-hand-side of an assignment in TP_fast_assign() only involved a simple variable assignment, but as Steve pointed out, some assignments are more complicated than that. For example, in the sched_switch tracepoint assignments: __entry->prev_prio = prev->prio; __entry->prev_state = __trace_sched_switch_state(prev); so the prev_prio should be able to be tested 'in-line' but the prev_state would require a temporary buffer to write the value into before doing the test as mentioned by Steve. At which point you're no further ahead (in that case) than the current situation... Tom > So I think it would be wise to make this change sooner rather than > later. -- 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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