> On Sep 14, 2023, at 10:22 PM, NeilBrown <neilb@xxxxxxx> wrote: > > > lwq is a FIFO single-linked queue that only requires a spinlock > for dequeueing, which happens in process context. Enqueueing is atomic > with no spinlock and can happen in any context. > > This is particularly useful when work items are queued from BH or IRQ > context, and when they are handled one at a time by dedicated threads. > > Avoiding any locking when enqueueing means there is no need to disable > BH or interrupts, which is generally best avoided (particularly when > there are any RT tasks on the machine). > > This solution is superior to using "list_head" links because we need > half as many pointers in the data structures, and because list_head > lists would need locking to add items to the queue. > > This solution is superior to a bespoke solution as all locking and > container_of casting is integrated, so the interface is simple. > > Despite the similar name, this solution meets a distinctly different > need to kfifo. kfifo provides a fixed sized circular buffer to which > data can be added at one end and removed at the other, and does not > provide any locking. lwq does not have any size limit and works with > data structures (objects?) rather than data (bytes). > > A unit test for basic functionality, which runs at boot time, is included. > > Signed-off-by: NeilBrown <neilb@xxxxxxx> Thank you for all of this work, Neil. The metrics in the cover letter speak for themselves. I've applied the series to nfsd-next and squashed this patch in. > --- > include/linux/lwq.h | 4 ++++ > lib/lwq.c | 4 ++++ > 2 files changed, 8 insertions(+) > > diff --git a/include/linux/lwq.h b/include/linux/lwq.h > index 52b9c81b493a..c4148fe1cf72 100644 > --- a/include/linux/lwq.h > +++ b/include/linux/lwq.h > @@ -7,6 +7,10 @@ > * > * Entries can be enqueued from any context with no locking. > * Entries can be dequeued from process context with integrated locking. > + * > + * This is particularly suitable when work items are queued in > + * BH or IRQ context, and where work items are handled one at a time > + * by dedicated threads. > */ > #include <linux/container_of.h> > #include <linux/spinlock.h> > diff --git a/lib/lwq.c b/lib/lwq.c > index 7fe6c7125357..eb8324225309 100644 > --- a/lib/lwq.c > +++ b/lib/lwq.c > @@ -8,6 +8,10 @@ > * Entries are dequeued using a spinlock to protect against > * multiple access. The llist is staged in reverse order, and refreshed > * from the llist when it exhausts. > + * > + * This is particularly suitable when work items are queued in > + * BH or IRQ context, and where work items are handled one at a time > + * by dedicated threads. > */ > #include <linux/rcupdate.h> > #include <linux/lwq.h> > -- > 2.42.0 > -- Chuck Lever
