Messages in this thread | | | From | Namhyung Kim <> | Subject | Re: [PATCH] perf record: mmap output file - v2 | Date | Wed, 16 Oct 2013 10:24:56 +0900 |
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Hi David,
On Tue, 15 Oct 2013 07:25:04 -0600, David Ahern wrote: > On 10/15/13 1:09 AM, Namhyung Kim wrote: >>> The stat() seems superfluous, here in __cmd_record() we've just checked >>> the output_name and made sure it exists. Can that stat() call ever fail? >> >> AFAICS it's needed to check current file size. But I think it's better >> to use fstat(). > > Sure fstat could be used over stat -- if it ends up staying. > > >>> >>> 3) >>> >>> The rec->bytes_at_mmap_start field feels a bit weird. If I read the code >>> correctly, in every 'perf record' invocation, rec->bytes_written starts at >>> 0 - i.e. we don't have repeat invocations of cmd_record(). >> >> rec->bytes_written is updated when it writes to the output file for >> synthesizing COMM/MMAP events (this mmap output is not used at that time). > > Ingo: I went through a number of itereations before using the > bytes_at_mmap_start. One of those was to use the bytes_written > counter. All failed. Header + synthesized events are written to the > file before we start farming the ring buffers. > > Perhaps a good code cleanup will help figure out why. I needed the > functionality ASAP for use with perf-trace -a so I stuck with the new > variable. Since this change is working out well, I will look at a code > clean up on the next round.
session->header.data_offset ?
> > I am traveling to LinuxCon / KVM Forum / Tracing Forum on > Friday. Perhaps the clean up and followup patch can be done on the > long plane ride; more likely when I return which means 3.14 material.
See you there :)
> >> Actually I worried about the mmap offset not being aligned to page >> size. But it seems that's not a problem. > > This code snippet makes sure the mmap offset is a multiple of 64M > (rec->mmap_size). offset is the argument to mmap; mmap_offset is the > where we are within the mmap for the next copy: > > + offset = rec->bytes_at_mmap_start + rec->bytes_written; > + if (offset < (ssize_t) rec->mmap_size) { > + rec->mmap_offset = offset; > + offset = 0; > + } else > + rec->mmap_offset = 0; >
Oh, I overlooked this code, it actually aligned offset.
Thanks, Namhyung
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