George Dunlap wrote:

There's no copying from the HV to the xentrace process. But there is
copying from xentrace to the dom0 kernel for the output file. Some
copying is necessary right now, because rather than writing out the
pages verbatim, xentrace writes out the pcpu before writing out each
record:
void write_rec(unsigned int cpu, struct t_rec *rec, FILE *out)
{
 size_t written = 0;
 written += fwrite(&cpu, sizeof(cpu), 1, out);
 written += fwrite(rec, sizeof(*rec), 1, out);
 if ( written != 2 )
 {
 PERROR("Failed to write trace record");
 exit(EXIT_FAILURE);
 }
}
If we wanted to make it zero copy all the way from the HV to the disk,
we could have the xentrace process one stream per cpu, and do
whatever's necessary to use DMA. (Does anyone know if O_DIRECT will

do direct DMA, or if one would have to use a raw disk?)

Rob
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel