Re: Problem with smbdirect rw credits and initiator_depth

[Stefan Metzmacher <metze@samba.org>]

Am 15.01.26 um 03:01 schrieb Namjae Jeon:
> On Thu, Jan 15, 2026 at 3:13 AM Stefan Metzmacher <metze@samba.org> wrote:
>>
>> Am 15.12.25 um 21:17 schrieb Stefan Metzmacher:
>>> Am 14.12.25 um 23:56 schrieb Stefan Metzmacher:
>>>> Am 13.12.25 um 03:14 schrieb Namjae Jeon:
>>>>>> I've put these changes a long with rw credit fixes into my
>>>>>> for-6.18/ksmbd-smbdirect-regression-v4 branch, are you able to
>>>>>> test this?
>>>>> Problems still occur. See:
>>>>
>>>> :-( Would you be able to use rxe and cake a network capture?
>>>>
>>>> Using test files with all zeros, e.g.
>>>> dd if=/dev/zero of=/tmp/4096MBzeros-sparse.dat seek=4096MB bs=1 count=1
>>>> would allow gzip --best on the capture file to compress well...
>>>
>>> I think I found something that explains it and
>>> I was able to reproduce and what I have in mind.
>>>
>>> We increment recv_io.posted.count after ib_post_recv()
>>>
>>> And manage_credits_prior_sending() uses
>>>
>>> new_credits = recv_io.posted.count - recv_io.credits.count
>>>
>>> But there is a race between the hardware receiving a message
>>> and recv_done being called in order to decrement recv_io.posted.count
>>> again. During that race manage_credits_prior_sending() might grant
>>> too much credits.
>>>
>>> Please test my for-6.18/ksmbd-smbdirect-regression-v5 branch,
>>> I haven't tested this branch yet, I'm running out of time
>>> for the day.
>>>
>>> But I tested it with smbclient and having a similar
>>> logic in fs/smb/common/smbdirect/smbdirect_connection.c
>>
>> I was able to reproduce the problem and the fix I created
>> for-6.18/ksmbd-smbdirect-regression-v5 was not correct.
>>
>> I needed to use
>>
>> available = atomic_xchg(&sc->recv_io.credits.available, 0);
>>
>> instead of
>>
>> available = atomic_read(&sc->recv_io.credits.available);
>> atomic_sub(new_credits, &sc->recv_io.credits.available);
>>
>> This following branch works for me:
>> for-6.18/ksmbd-smbdirect-regression-v7
>> and with the fixes again master this should also work:
>> for-6.19/ksmbd-smbdirect-regression-v1
>>
>> I'll post real patches tomorrow.
>>
>> Please check.
> Okay, I will test it with two branches.
> I'll try it too, but I recommend running frametest for performance
> difference and stress testing.
> 
> https://support.dvsus.com/hc/en-us/articles/212925466-How-to-use-frametest
> 
> ex) frametest.exe -w 4k -t 20 -n 2000

That works fine, but

  frametest.exe -r 4k -t 20 -n 2000

generates a continues stream of such messages:
ksmbd: Failed to send message: -107

Both with 6.17.2 and for-6.19/ksmbd-smbdirect-regression-v1,
so this is not a regression.

I'll now check if the is related to the other problems
I found and fixes in for-6.18/ksmbd-smbdirect-regression-v5

metze