RE: [PATCH V5 3/5] RDMA/iser: Limit sg tablesize and max_sectors to device fastreg max depth

["Steve Wise" <swise-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org>]

> -----Original Message-----
> From: Sagi Grimberg [mailto:sagig-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org]
> Sent: Monday, July 06, 2015 2:51 AM
> To: Steve Wise; dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org
> Cc: infinipath-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org; sagig-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org; ogerlitz-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org; roid-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org; linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org;
> eli-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org; target-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Subject: Re: [PATCH V5 3/5] RDMA/iser: Limit sg tablesize and max_sectors to device fastreg max depth
> 
> On 7/5/2015 8:44 PM, Steve Wise wrote:
> > Currently the sg tablesize, which dictates fast register page list
> > depth to use, does not take into account the limits of the rdma device.
> > So adjust it once we discover the device fastreg max depth limit.  Also
> > adjust the max_sectors based on the resulting sg tablesize.
> >
> > Signed-off-by: Steve Wise <swise-7bPotxP6k4+P2YhJcF5u+vpXobYPEAuW@public.gmane.org>
> > ---
> >
> >   drivers/infiniband/ulp/iser/iscsi_iser.c |    9 +++++++++
> >   1 files changed, 9 insertions(+), 0 deletions(-)
> >
> > 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.

  

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