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SubjectRe: [PATCH v2 0/6] Corrections to cpu map event encoding
Em Sun, Aug 14, 2022 at 04:05:19PM -0700, Ian Rogers escreveu:
> Hi,
>
> It looks like we missed this one. Can it get into the next PR as a fix?

I've queued up to 4/6 for perf/urgent, 5 and 6 will go to perf/core once
I merge perf/urgent there, i.e. after I send this to Linus.

- Arnaldo

> Thanks,
> Ian
>
>
> On Thu, Aug 4, 2022 at 1:23 PM Jiri Olsa <olsajiri@gmail.com> wrote:
>
> > On Tue, Jun 14, 2022 at 07:33:47AM -0700, Ian Rogers wrote:
> > > A mask encoding of a cpu map is laid out as:
> > > u16 nr
> > > u16 long_size
> > > unsigned long mask[];
> > > However, the mask may be 8-byte aligned meaning there is a 4-byte pad
> > > after long_size. This means 32-bit and 64-bit builds see the mask as
> > > being at different offsets. On top of this the structure is in the byte
> > > data[] encoded as:
> > > u16 type
> > > char data[]
> > > This means the mask's struct isn't the required 4 or 8 byte aligned, but
> > > is offset by 2. Consequently the long reads and writes are causing
> > > undefined behavior as the alignment is broken.
> > >
> > > These changes do minor clean up with const, visibility of functions
> > > and using the constant time max function. It then adds 32 and 64-bit
> > > mask encoding variants, packed to match current alignment. Taking the
> > > address of a packed struct leads to unaligned data, so function
> > > arguments are altered to be passed the packed struct. To compact the
> > > mask encoding further and drop the padding, the 4-byte variant is
> > > preferred. Finally a new range encoding is added, that reduces the
> > > size of the common case of a range of CPUs to a single u64.
> > >
> > > On a 72 CPU (hyperthread) machine the original encoding of all CPUs is:
> > > 0x9a98 [0x28]: event: 74
> > > .
> > > . ... raw event: size 40 bytes
> > > . 0000: 4a 00 00 00 00 00 28 00 01 00 02 00 08 00 00 00
> > J.....(.........
> > > . 0010: 00 00 ff ff ff ff ff ff ff ff ff 00 00 00 00 00
> > ................
> > > . 0020: 00 00 00 00 00 00 00 00 ........
> >
> > >
> > > 0 0 0x9a98 [0x28]: PERF_RECORD_CPU_MAP
> > >
> > > Using the 4-byte encoding it is:
> > > 0x9a98@pipe [0x20]: event: 74
> > > .
> > > . ... raw event: size 32 bytes
> > > . 0000: 4a 00 00 00 00 00 20 00 01 00 03 00 04 00 ff ff J.....
> > .........
> > > . 0010: ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 00
> > ................
> > >
> > > 0 0 0x9a98 [0x20]: PERF_RECORD_CPU_MAP
> > >
> > > Finally, with the range encoding it is:
> > > 0x9ab8@pipe [0x10]: event: 74
> > > .
> > > . ... raw event: size 16 bytes
> > > . 0000: 4a 00 00 00 00 00 10 00 02 00 00 00 00 00 47 00
> > J.............G.
> > >
> > > 0 0 0x9ab8 [0x10]: PERF_RECORD_CPU_MAP
> > >
> > > v2. Fixes a bug in the size computation of the update header
> > > introduced by the last patch (Add range data encoding) and caught
> > > by address sanitizer.
> > >
> > > Ian Rogers (6):
> > > perf cpumap: Const map for max
> > > perf cpumap: Synthetic events and const/static
> > > perf cpumap: Compute mask size in constant time
> > > perf cpumap: Fix alignment for masks in event encoding
> > > perf events: Prefer union over variable length array
> > > perf cpumap: Add range data encoding
> >
> > Acked-by: Jiri Olsa <jolsa@kernel.org>
> >
> > thanks,
> > jirka
> >
> > >
> > > tools/lib/perf/cpumap.c | 2 +-
> > > tools/lib/perf/include/perf/cpumap.h | 2 +-
> > > tools/lib/perf/include/perf/event.h | 61 ++++++++-
> > > tools/perf/tests/cpumap.c | 71 ++++++++---
> > > tools/perf/tests/event_update.c | 14 +--
> > > tools/perf/util/cpumap.c | 111 +++++++++++++---
> > > tools/perf/util/cpumap.h | 4 +-
> > > tools/perf/util/event.h | 4 -
> > > tools/perf/util/header.c | 24 ++--
> > > tools/perf/util/session.c | 35 +++---
> > > tools/perf/util/synthetic-events.c | 182 +++++++++++++--------------
> > > tools/perf/util/synthetic-events.h | 2 +-
> > > 12 files changed, 327 insertions(+), 185 deletions(-)
> > >
> > > --
> > > 2.36.1.476.g0c4daa206d-goog
> > >
> >

--

- Arnaldo

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