Re: [PATCH v11 0/4] Introducing a queue read/write lock implementation

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 01/31/2014 04:26 AM, Peter Zijlstra wrote:
On Thu, Jan 30, 2014 at 04:17:15PM +0100, Peter Zijlstra wrote:
The below is still small and actually works.
OK, so having actually worked through the thing; I realized we can
actually do a version without MCS lock and instead use a ticket lock for
the waitqueue.

This is both smaller (back to 8 bytes for the rwlock_t), and should be
faster under moderate contention for not having to touch extra
cachelines.

Completely untested and with a rather crude generic ticket lock
implementation to illustrate the concept:


Using a ticket lock instead will have the same scalability problem as the ticket spinlock as all the waiting threads will spin on the lock cacheline causing a lot of cache bouncing traffic. That is the reason why I want to replace ticket spinlock with queue spinlock. If the 16-byte size is an issue, I can use the same trick in the queue spinlock patch to reduce its size down to 8 bytes with a bit more overhead in the slowpath.

Another thing I want to discuss about is whether a bit more overhead in moderate contention cases is really such a bit deal. With moderate contention, I suppose the amount of time spent in the locking functions will be just a few percent at most for real workloads. It won't really be noticeable if the locking functions take, maybe, 50% more time to finish. Anyway, I am going to do more performance testing on low end machines.

-Longman
--
To unsubscribe from this list: send the line "unsubscribe linux-arch" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Linux Kernel]     [Kernel Newbies]     [x86 Platform Driver]     [Netdev]     [Linux Wireless]     [Netfilter]     [Bugtraq]     [Linux Filesystems]     [Yosemite Discussion]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Device Mapper]

  Powered by Linux