Re: [Xen-devel] Hi,something about the xentrace tool

To:	"Rob Gardner" <rob.gardner@xxxxxx>
Subject:	Re: [Xen-devel] Hi,something about the xentrace tool
From:	"George Dunlap " <dunlapg@xxxxxxxxx>
Date:	Thu, 15 Jun 2006 14:20:15 -0400
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On 6/15/06, Rob Gardner <rob.gardner@xxxxxx> wrote:

I wouldn't call the amount of data 'huge'. Even on a very busy system,
where there are thousands of trace records being generated every second,
that's still a pretty small amount of data. (The size of a trace record
is something like 50 or 60 bytes.)


For the record, I think the trace record size in the trace buffers is
probably 32 bytes:

struct {
  unsigned long long rdtsc;  /* 8 */
  unsigned long event; /* + 4 = 12 */
  unsigned long data[5] /* + (4 * 5) = 32 */
};

The size on disk from xentrace is 36 bytes (it adds 4 bytes for the cpu).

If someone were really worried about copy time, one could write
something which uses raw disks (or, perhaps, the O_DIRECT flag) to DMA
data straight from the buffers to the disk.  But I'm not really
worried about it at this point. :-)

Peace,
-George

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Re: [Xen-devel] Hi,something about the xentrace tool