Messages in this thread | | | Subject | Re: [PATCH] RDMA/core: reduce IB_POLL_BATCH constant | From | Max Gurtovoy <> | Date | Wed, 21 Feb 2018 11:47:56 +0200 |
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On 2/20/2018 11:47 PM, Chuck Lever wrote: > > >> On Feb 20, 2018, at 4:14 PM, Bart Van Assche <Bart.VanAssche@wdc.com> 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 > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-rdma" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
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