plz unscrible my email from this list. thanks. On Wed, Nov 26, 2008 at 11:22 PM, Elad Lahav < [EMAIL PROTECTED]> wrote:
> I am looking into some scalability issues on a 4-way Xeon machine (4 > separate CPUs, not cores). I believe I have tracked down the problem to bus > contention: OProfile results suggest a strong correlation between > instructions reporting a high number of global_power_events and > FSB_data_activity events. > Some of these events can be easily explained. However, what surprises me, > is that certain lock operations seem to cause considerable lock activity. > For example, a call to spin_unlock_irqsave() from e1000_xmit_frame(). The > strange thing about it is that the experiments I am conducting strictly > partition the NICs among the CPUs (interrupt and process affinity), so that > there is no contention on the lock (verified with lockstat). > My understanding suggests that the variable of a lock that is only accessed > by a single CPU should be constantly in the CPU's cache in Modified mode, as > no other CPU is ever invalidating it, and thus there should be little if any > FSB activity due to access to this variable. It should be noted that the > number of FSB events per-cpu increases considerably when moving from 3 to 4 > CPUs, while the number of cache misses stays roughly the same. > Is my understanding correct? Are there any other reasons for FSB activity > related to locks? > > --Elad > > > -- > To unsubscribe from this list: send an email with > "unsubscribe kernelnewbies" to [EMAIL PROTECTED] > Please read the FAQ at http://kernelnewbies.org/FAQ > >
