On 11/25/2014 12:22 PM, Khalid Aziz wrote: > On 11/25/2014 08:25 AM, Rik van Riel wrote: >> On 11/25/2014 09:52 AM, Khalid Aziz wrote: >>> On 11/24/2014 07:03 PM, Rik van Riel wrote: >>>> -----BEGIN PGP SIGNED MESSAGE----- >>>> Hash: SHA1 >>>> >>>> On 11/24/2014 03:56 PM, Khalid Aziz wrote: >>>>> sched/fair: Add advisory flag for borrowing a timeslice >>>>> >>>>> This patch adds a way for a task to request to borrow one >>>>> timeslice from future if it is about to be preempted, so it could >>>>> delay preemption and complete any critical task it is in the middle >>>>> of. >>>>> >>>>> This feature helps with performance on databases and has been used >>>>> for many years on other OSs by the databases. This feature helps in >>>>> situation where a task acquires a lock before performing a critical >>>>> operation on the database and happens to get preempted >>>> >>>> Why don't the other tasks that want the lock sleep on the >>>> lock? >>>> >>>> I can see this "solution" help mostly with userspace spinlocks, >>>> which are relics of a past era that need to die. There is no >>>> way userspace spinlocks will not fail miserably on virtual >>>> machines, and it is time to get rid of them. >>> >>> This solution indeed is for userspace spinlocks. Database code has been >>> written with all critical locking implemented in userspace (as I have >>> been told by database folks. I am not a database guy). >> >> They should fix that. > > Agreed, but that is a very large task for databases for sure and > potentially for java as well (think exhaustive testing as well besides > code re-write). I do not see this happening except as part of major > re-architecture. In the mean time, if we can give them help without > impacting kernel significantly for other users, it only makes Linux a > more usable platform for them. I am not convinced that permanently adding overhead to the Linux scheduler in order to deal with a temporary problem in database and Java software (probably not every JVM, either!) is a worthwhile trade-off.. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
