On Tue, Jun 11, 2013 at 03:53:17PM +0800, Lai Jiangshan wrote: > On 06/11/2013 08:51 AM, Linus Torvalds wrote: > > On Mon, Jun 10, 2013 at 5:44 PM, Steven Rostedt <rost...@goodmis.org> wrote: > >> > >> OK, I haven't found a issue here yet, but youss are beiing trickssy! We > >> don't like trickssy, and we must find precccciouss!!! > > > > .. and I personally have my usual reservations. I absolutely hate > > papering over scalability issues, and historically whenever people > > have ever thought that we want complex spinlocks, the problem has > > always been that the locking sucks. > > > > So reinforced by previous events, I really feel that code that needs > > this kind of spinlock is broken and needs to be fixed, rather than > > actually introduce tricky spinlocks. > > > > So in order to merge something like this, I want (a) numbers for real > > loads and (b) explanations for why the spinlock users cannot be fixed. > > > > Because "we might hit loads" is just not good enough. I would counter > > with "hiding problems causes more of them". > > > > Hi, all > > Off-topic, although I am in this community for several years, > I am not exactly clear with this problem. > > 1) In general case, which lock is the most competitive in the kernel? what it > protects for? > 2) In which special case, which lock is the most competitive in the kernel? > what it protects for? > 3) In general case, which list is the most hot list? > 4) In which special case, which list is the most hot list?
Others would know better than I, but mmap_sem has been called out as a prime offender for some workloads. There is of course some debate as to whether the fault lies mmap_sem or with the workloads. There have been some efforts to solve this one on LKML, plus some in academia have worked on this as well: http://people.csail.mit.edu/nickolai/papers/clements-bonsai.pdf http://pdos.csail.mit.edu/papers/radixvm:eurosys13.pdf And IIRC this was the subject of a session at a recent minisummit. There are a few locks within the RCU implementation that have popped up from time to time on very large systems, but I have dealt with those and have plans for each should it become a problem. The plans probably won't survive first contact with a real workload, but having thought things through is very helpful. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/