On 2/20/2018 11:47 PM, Chuck Lever wrote:
On Feb 20, 2018, at 4:14 PM, Bart Van Assche <Bart.VanAssche@xxxxxxx> wrote:
On Tue, 2018-02-20 at 21:59 +0100, Arnd Bergmann wrote:
/* # of WCs to poll for with a single call to ib_poll_cq */
-#define IB_POLL_BATCH 16
+#define IB_POLL_BATCH 8
The purpose of batch polling is to minimize contention on the cq spinlock.
Reducing the IB_POLL_BATCH constant may affect performance negatively. Has
the performance impact of this change been verified for all affected drivers
(ib_srp, ib_srpt, ib_iser, ib_isert, NVMeOF, NVMeOF target, SMB Direct, NFS
over RDMA, ...)?
Only the users of the DIRECT polling method use an on-stack
array of ib_wc's. This is only the SRP drivers.
The other two modes have use of a dynamically allocated array
of ib_wc's that hangs off the ib_cq. These shouldn't need any
reduction in the size of this array, and they are the common
case.
IMO a better solution would be to change ib_process_cq_direct
to use a smaller on-stack array, and leave IB_POLL_BATCH alone.
Yup, good idea.
you can define IB_DIRECT_POLL_BATCH to be 8 and use it in
ib_process_cq_direct. *but* please make sure to use the right value in
ib_poll_cq since the wcs array should be able to hold the requested
amount of wcs.
-Max.
--
Chuck Lever
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