Re: Hi,something about the xentrace tool

[Rob Gardner <rob.gardner@hp.com>]

George Dunlap wrote:
> On 6/15/06, Rob Gardner <rob.gardner@hp.com> 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:

You're right, I was thinking everything is 64 bits these days. In any 
case, it's a small amount of data.

> 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.  

Once again, there is no explicit copying of the data between kernel and 
user space, so nobody should be worried about it.

Rob