Re: [PATCH v1 03/12] xprtrdma: Increase default credit limit

Chuck Lever
2015-07-10T14:33:22Z

On Jul 10, 2015, at 6:45 AM, Devesh Sharma <devesh.sharma-1wcpHE2jlwO1Z/+hSey0Gg@public.gmane.org> wrote:

> Increasing the default slot table entries will increase the MR
> requirements per mount.

Yes, but:

> Currently, with 32 as default Client ends up allocating 2178 frmrs
> (ref: kernel 4.1-rc4) for a single mount. With 128 frmr requirement
> for startup would be 8448.

Commit 40c6ed0c8a7f ("xprtrdma: Reduce per-transport MR allocation”)
is supposed to address this. This commit is in 4.1.

The number of MRs per credit is now 256 divided by the HCA’s
max_fast_reg_page_list_len. See frwr_op_open().

For mlx4 the number of MRs per credit is just 1, for example.

> 8K+ MRs per mount just for start-up, I am a little doubtful about this
> change. We can always release-note that "for better performance
> increase the slot table entries by echo 128 >
> /proc/sys/sunrpc/rdma_slot_table_entries"
>
> -Regards
> Devesh
>
> On Fri, Jul 10, 2015 at 2:12 AM, Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org> wrote:
>> In preparation for similar increases on NFS/RDMA servers, bump the
>> advertised credit limit for RPC/RDMA to 128. This allocates some
>> extra resources, but the client will continue to allow only the
>> number of RPCs in flight that the server requests via its advertised
>> credit limit.
>>
>> Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
>> ---
>> include/linux/sunrpc/xprtrdma.h | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/linux/sunrpc/xprtrdma.h b/include/linux/sunrpc/xprtrdma.h
>> index b176130..b7b279b 100644
>> --- a/include/linux/sunrpc/xprtrdma.h
>> +++ b/include/linux/sunrpc/xprtrdma.h
>> @@ -49,7 +49,7 @@
>> * a single chunk type per message is supported currently.
>> */
>> #define RPCRDMA_MIN_SLOT_TABLE (2U)
>> -#define RPCRDMA_DEF_SLOT_TABLE (32U)
>> +#define RPCRDMA_DEF_SLOT_TABLE (128U)
>> #define RPCRDMA_MAX_SLOT_TABLE (256U)
>>
>> #define RPCRDMA_DEF_INLINE (1024) /* default inline max */
>>
>> --
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--
Chuck Lever