On 7/7/2015 6:41 PM, Steve Wise wrote:
-----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()...
I guess the min is fine given that I have a patchset for 8MB support,
so we'll get it right then.
Sagi.
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