On Wed, Apr 29, 2015 at 2:43 PM, Meng Xu <xumengpa...@gmail.com> wrote: > > > 2015-04-28 22:46 GMT-04:00 Xuehan Xu <xxhdx1985...@gmail.com>: > >> ---------- Forwarded message ---------- >> From: "Xuehan Xu" <xxhdx1985...@gmail.com> >> Date: Apr 29, 2015 10:11 AM >> Subject: How to get real time in a xen vm? >> To: <xs-de...@lists.xenserver.org> >> Cc: >> >> Hi, everyone >> >> Recently, I got a need to measure the latency of the I/O operation of >> TAPDISK on dom0, in comparison with that latency on a phyisical machine. >> >> I tried to measure the latency by calling "gettimeofday" right before and >> after the io operation and compute the difference. But the time acquired by >> gettimeofday is a virtual time of the dom0, which makes it meaningless to >> compare to the latency on a physical machine. >> >> How can I get the real and highly accurate time in dom0? Thanks:) > > > You may want to try the instruction 'rdtsc' to read the timestamp counter > register to get the latency.
Also, you probably want to set the TSC mode to "never emulate". See http://xenbits.xen.org/docs/4.5-testing/misc/tscmode.txt -George _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
