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Date: Wed, 11 Nov 2009 15:32:28 -0200 From: Arnaldo Carvalho de Melo <acme@...hat.com> To: Frederic Weisbecker <fweisbec@...il.com> Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>, Mike Galbraith <efault@....de>, Paul Mackerras <paulus@...ba.org>, Hitoshi Mitake <mitake@....info.waseda.ac.jp> Subject: Re: [PATCH 6/6] perf tools: Bring linear set of section headers for features Em Wed, Nov 11, 2009 at 05:49:37PM +0100, Frederic Weisbecker escreveu: > On Wed, Nov 11, 2009 at 07:20:04AM +0100, Peter Zijlstra wrote: > > On Wed, 2009-11-11 at 04:51 +0100, Frederic Weisbecker wrote: > > > Build a set of section headers for features right after the datas. > > > Each implemented feature will have one of such section header that > > > provides the offset and the size of the data manipulated by the feature. > > > > > > The trace informations have moved after the data and are recorded > > > on exit time. > > > > > > The new layout is as follows: > > > > > > ----------------------- > > > ___ > > > [ magic ] | > > > [ header size ] | > > > [ attr size ] | > > > [ attr content offset ] | > > > [ attr content size ] | > > > [ data offset ] File Headers > > > [ data size ] | > > > [ event_types offset ] | > > > [ event_types size ] | > > > [ feature bitmap ] v > > > > > > [ attr section ] > > > [ events section ] > > > > > > ___ > > > [ X ] | > > > [ X ] | > > > [ X ] Datas > > > [ X ] | > > > [ X ] v > > > > > > ___ > > > [ Feature 1 offset ] | > > > [ Feature 1 size ] Features headers > > > [ Feature 2 offset ] | > > > [ Feature 2 size ] v > > > > > > [ Feature 1 content ] > > > [ Feature 2 content ] > > > ----------------------- > > > > > > We have as many feature's section headers as we have features in use for > > > the current file. > > > > > > Say Feat 1 and Feat 3 are used by the file, but not Feat 2. Then the > > > feature headers will be like follows: > > > > > > [ Feature 1 offset ] | > > > [ Feature 1 size ] Features headers > > > [ Feature 3 offset ] | > > > [ Feature 3 size ] v > > > > > > There is no hole to cover Feature 2 that is not in use here. We only > > > need to cover the needed headers in order, from the lowest feature bit > > > to the highest. > > > > > > Currently we have two features: HEADER_TRACE_INFO and HEADER_BUILD_ID. > > > Both have their contents that follow the feature headers. Putting the > > > contents right after the feature headers is not mandatory though. > > > While we keep the feature headers right after the data and in order, > > > their offsets can point everywhere. We have just put the two above > > > feature contents in the end of the file for convenience. > > > > > > The purpose of this layout change is to have a file format that scales > > > while keeping it simple: having such linear feature headers is less > > > error prone wrt forward/backward compatibility as the content of a > > > feature can be put anywhere, its location can even change by the > > > time, it's fine because its headers will tell where it is. And we know > > > how to find these headers, following the above rules. > > > > Does do mess up append though... be sure to add some magic for that. > > Yep. It seems to work. What happens is that trace information are > re-computed. The same goes for build id I guess. Well, we would need to get the existing buildids, insert them into the dsos list, and as we use dsos__findnew DSOs already in the list wouldn't be added, and at the end we would, as you say, recompute the buildid table. > What happens is that the appended datas override the features sections > and headers, but this is fine because we rewrite them in the end. > > But these both need to support appending mode internally (ie: append > the new informtions on top of exisiting ones instead of redo the whole) > and then rewrite the whole at exit like it's done currently. yeah. - Arnado -- 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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