lkml.org 
[lkml]   [2009]   [Nov]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [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


    \
     
     \ /
      Last update: 2009-11-11 18:35    [W:0.075 / U:0.164 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site