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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
Cc: xen-tools@xxxxxxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx, xen-users@xxxxxxxxxxxxxxxxxxx, rickey berkeley <rickey.berkeley@xxxxxxxxx>
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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. :-)


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