Re: performance regression noted in v5.11-rc after c062db039f40

[Chuck Lever <chuck.lever@oracle.com>]

> On Jan 18, 2021, at 8:22 PM, Lu Baolu <baolu.lu@linux.intel.com> wrote:
> 
> Do you mind posting the cap and ecap of the iommu used by your device?
> 
> You can get it via sysfs, for example:
> 
> /sys/bus/pci/devices/0000:00:14.0/iommu/intel-iommu# ls
> address  cap  domains_supported  domains_used  ecap  version

[root@manet intel-iommu]# lspci | grep Mellanox
03:00.0 Network controller: Mellanox Technologies MT27520 Family [ConnectX-3 Pro]
[root@manet intel-iommu]# pwd
/sys/devices/pci0000:00/0000:00:03.0/0000:03:00.0/iommu/intel-iommu
[root@manet intel-iommu]# for i in *; do   echo -n $i ": ";   cat $i; done
address : c7ffc000
cap : d2078c106f0466
domains_supported : 65536
domains_used : 62
ecap : f020de
version : 1:0
[root@manet intel-iommu]#


>> Fwiw, this system uses the Intel C612 chipset with Intel(R) Xeon(R)
>> E5-2603 v3 @ 1.60GHz CPUs.
> 
> Can you please also hack a line of code to check the return value of
> iommu_dma_map_sg()?

diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_ops.c
index baca49fe83af..e811562ead0e 100644
--- a/net/sunrpc/xprtrdma/frwr_ops.c
+++ b/net/sunrpc/xprtrdma/frwr_ops.c
@@ -328,6 +328,7 @@ struct rpcrdma_mr_seg *frwr_map(struct rpcrdma_xprt *r_xprt,
 
        dma_nents = ib_dma_map_sg(ep->re_id->device, mr->mr_sg, mr->mr_nents,
                                  mr->mr_dir);
+       trace_printk("ib_dma_map_sg(%d) returns %d\n", mr->mr_nents, dma_nents);
        if (!dma_nents)
                goto out_dmamap_err;
        mr->mr_device = ep->re_id->device;

During the 256KB iozone test I used before, this trace log is generated:

   kworker/u28:3-1269  [000]   336.054743: bprint:               frwr_map: ib_dma_map_sg(30) returns 1
   kworker/u28:3-1269  [000]   336.054835: bprint:               frwr_map: ib_dma_map_sg(30) returns 1
   kworker/u28:3-1269  [000]   336.055022: bprint:               frwr_map: ib_dma_map_sg(4) returns 1
   kworker/u28:3-1269  [000]   336.055118: bprint:               frwr_map: ib_dma_map_sg(30) returns 1
   kworker/u28:3-1269  [000]   336.055312: bprint:               frwr_map: ib_dma_map_sg(30) returns 1
   kworker/u28:3-1269  [000]   336.055407: bprint:               frwr_map: ib_dma_map_sg(4) returns 1

--
Chuck Lever