linux-kernel - Re: [PATCH 18/18] 2.6.17.9 perfmon2 patch for review: new x86

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Message-ID: <20060823155321.GD1733@frankl.hpl.hp.com>
Date:	Wed, 23 Aug 2006 08:53:21 -0700
From:	Stephane Eranian <eranian@....hp.com>
To:	Christoph Hellwig <hch@...radead.org>, Andi Kleen <ak@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 18/18] 2.6.17.9 perfmon2 patch for review: new x86_64 files

Christoph,

On Wed, Aug 23, 2006 at 04:25:55PM +0100, Christoph Hellwig wrote:
> On Wed, Aug 23, 2006 at 03:29:32AM -0700, Stephane Eranian wrote:
> > > > +#define PFM_EM64T_PEBS_SMPL_UUID { \
> > > > +	0x36, 0xbe, 0x97, 0x94, 0x1f, 0xbf, 0x41, 0xdf,\
> > > > +	0xb4, 0x63, 0x10, 0x62, 0xeb, 0x72, 0x9b, 0xad}
> > > 
> > > What does it need the UUID for?
> > > 
> > Every sampling format is identified by a UUID. This  is how an
> > application can identify the format it wants to use when it
> > creates a context.
> 
> Please use a string name, just like every other interface for
> such selections.

What are the advantages at the syscall level (i.e., copy_user, 
format parsing) compared to a 16-entry byte array?

We are passing that uuid into a struct:

struct pfarg_ctx {
        __u8		ctx_smpl_buf_id[16];
        __u32		ctx_flags;
        __s32           ctx_fd;
        __u64           ctx_smpl_buf_size;
        __u64           ctx_reserved3[12];
};

-- 
-Stephane
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