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