----- Original Message ----- > From: "Josh Triplett" <[email protected]> > To: "Peter Zijlstra" <[email protected]> > Cc: "Paul E. McKenney" <[email protected]>, > [email protected], [email protected], > [email protected], [email protected], [email protected], > "mathieu desnoyers" > <[email protected]>, [email protected], [email protected], > [email protected], [email protected], > [email protected], [email protected], [email protected], "bobby prani" > <[email protected]> > Sent: Saturday, February 21, 2015 1:04:28 AM > Subject: Re: [PATCH tip/core/rcu 0/4] Programmatic nestable expedited grace > periods > > On Fri, Feb 20, 2015 at 05:54:09PM +0100, Peter Zijlstra wrote: > > On Fri, Feb 20, 2015 at 08:37:37AM -0800, Paul E. McKenney wrote: > > > On Fri, Feb 20, 2015 at 10:11:07AM +0100, Peter Zijlstra wrote: > > > > Does it really make a machine boot much faster? Why are people using > > > > synchronous gp primitives if they care about speed? Should we not fix > > > > that instead? > > > > > > The report I heard was that it provided 10-15% faster boot times. > > > > That's not insignificant; got more details? I think we should really > > look at why people are using the sync primitives. > > Paul, what do you think about adding a compile-time debug option to > synchronize_rcu() that causes it to capture the time on entry and exit > and print the duration together with the file:line of the caller? > Similar to initcall_debug, but for blocking calls to synchronize_rcu(). > Put that together with initcall_debug, and you'd have a pretty good idea > of where that holds up boot. > > We do want early boot to run as asynchronously as possible, and to avoid > having later bits of boot waiting on a synchronize_rcu from earlier bits > of boot. Switching a caller over to call_rcu() doesn't actually help if > it still has to finish a grace period before it can allow later bits to > run. Ideally, we ought to be able to work out the "depth" of boot in > grace-periods. > > Has anyone wired initcall_debug up to a bootchart-like graph?
The information about begin/end of synchronize_rcu, as well as begin/end of rcu_barrier() seems to be very relevant here. This should perhaps be covered tracepoints ? Isn't it already ? Thanks, Mathieu > > - Josh Triplett > -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
