Messages in this thread | | | Date | Wed, 28 May 2008 23:38:01 -0700 | From | Andrew Morton <> | Subject | Re: block: make blktrace use per-cpu buffers for message notes |
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On Thu, 29 May 2008 08:22:15 +0200 Jens Axboe <jens.axboe@oracle.com> wrote:
> On Wed, May 28 2008, Andrew Morton wrote: > > On Wed, 28 May 2008 15:59:07 GMT Linux Kernel Mailing List <linux-kernel@vger.kernel.org> wrote: > > > > > Gitweb: http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=64565911cdb57c2f512a9715b985b5617402cc67 > > > Commit: 64565911cdb57c2f512a9715b985b5617402cc67 > > > Parent: 4722dc52a891ab6cb2d637ddb87233e0ce277827 > > > Author: Jens Axboe <jens.axboe@oracle.com> > > > AuthorDate: Wed May 28 14:45:33 2008 +0200 > > > Committer: Jens Axboe <jens.axboe@oracle.com> > > > CommitDate: Wed May 28 14:49:27 2008 +0200 > > > > please try to avoid merging unreviewed changes. > > Just because you didn't review it doesn't mean it's unreviewed :-) > > It's not unreviewed, it was posted on lkml and a few version were > bounced back and forth.
OK. The Subject: swizzling confounded me.
> > > if (unlikely(bt)) \ > > > __trace_note_message(bt, fmt, ##__VA_ARGS__); \ > > > } while (0) > > > -#define BLK_TN_MAX_MSG 1024 > > > +#define BLK_TN_MAX_MSG 128 > > > > It seems a bit strange to do this right when we've taken this _off_ the > > stack. But I suppose nothing will break. > > It was never on the stack, it was a global static char array. We are > still allocating memory for this, per-cpu. So I think it still makes > sense to shrink the size. It's really meant for small trace messages, > 128 bytes is plenty. It's an in-kernel property, the userland app > doesn't care. So we could easily grow this in the future, should the > need arise.
yup.
It's a bit sad to stage the data in a local per-cpu buffer and then copy it into relay's per-cpu buffer. I guess this is because the length of the output isn't known beforehand. Could be fixed by doing what kvasprintf() does, but that might well be slower.
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