> -----Original Message----- > From: linux-rdma-owner@xxxxxxxxxxxxxxx [mailto:linux-rdma-owner@xxxxxxxxxxxxxxx] On Behalf Of Or Gerlitz > Sent: Tuesday, July 07, 2015 9:32 AM > To: Steve Wise; 'Sagi Grimberg' > Cc: dledford@xxxxxxxxxx; infinipath@xxxxxxxxx; roid@xxxxxxxxxxxx; linux-rdma@xxxxxxxxxxxxxxx; eli@xxxxxxxxxxxx; target- > devel@xxxxxxxxxxxxxxx > Subject: Re: [PATCH V5 3/5] RDMA/iser: Limit sg tablesize and max_sectors to device fastreg max depth > > On 7/7/2015 4:59 PM, Steve Wise wrote: > >>>>> > >>>diff --git a/drivers/infiniband/ulp/iser/iscsi_iser.c b/drivers/infiniband/ulp/iser/iscsi_iser.c > >>>>> > >>>index 6a594aa..de8730d 100644 > >>>>> > >>>--- a/drivers/infiniband/ulp/iser/iscsi_iser.c > >>>>> > >>>+++ b/drivers/infiniband/ulp/iser/iscsi_iser.c > >>>>> > >>>@@ -640,6 +640,15 @@ iscsi_iser_session_create(struct iscsi_endpoint *ep, > >>>>> > >>> SHOST_DIX_GUARD_CRC); > >>>>> > >>> } > >>>>> > >>> > >>>>> > >>>+ /* > >>>>> > >>>+ * Limit the sg_tablesize and max_sectors based on the device > >>>>> > >>>+ * max fastreg page list length. > >>>>> > >>>+ */ > >>>>> > >>>+ shost->sg_tablesize = min_t(unsigned short, shost->sg_tablesize, > >>>>> > >>>+ ib_conn->device->dev_attr.max_fast_reg_page_list_len); > >>>>> > >>>+ shost->max_sectors = min_t(unsigned int, > >>>>> > >>>+ 1024, (shost->sg_tablesize * PAGE_SIZE) >> 9); > >>>>> > >>>+ > >>>> > >> > >>>> > >>The min statement is meaningless for max_sectors - you do a min between > >>>> > >>default sg_tablesize and frpl length - so the maximum sg_tablesize is > >>>> > >>128 which is 1024 max_sectors. > >>> > > > >>> > >I'm not following. What if ib_conn->device->dev_attr.max_fast_reg_page_list_len is say, 32? > >>> > >Then shost->sg_tablesize is set to 32, and max_sectors is set to (32*4K) >> 9 == 256 512B sectors. > >> > > >> >Correct - but it cannot exceed 1024 (as it is derived from sg_tablesize > >> >which is maximum 128). > > Actually it is initialized to 1024 in iscsi_iser_sht / iscsi_iser.c, so it isn't derived from sg_tables (although it probably should be). I can > remove the min_t() though. > > > > Hey Or, thoughts? > > Originally, we've put the double restriction of 128 SG entries AND 1024 > sectors to make sure that whatever SG is up there, it'snot spanning > > 512KB. > > Think on SG whose one/some of their element/s is > one page or on > systems with > 4KB page size or others examples... since your patch > touched the number of SG entries I was thinking you need to make sure no > regression was introduced re the max_sectors to be <= 1024 > > If U2 are @ consensus that this is the case with the original patch w.o > further changes, let it be. > I'm not sure... you guys are the iSER experts. :) But considering a 64K PAGE_SIZE and an adjusted sg_tablesize of say, 32, w/o the min() we get (32 * 65536) >> 9 == 4096. So if the requirement is that max_sectors always be <= 1024, then we need the min()... Steve. -- To unsubscribe from this list: send the line "unsubscribe target-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
