netdev - Re: [PATCH net-next 3/7] net/rds: Wait for the FRMR_IS_FREE (or FRMR_IS_STALE) transition after posting IB_WR_LOCAL

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Date:   Mon, 1 Jul 2019 14:00:37 -0700
From:   santosh.shilimkar@...cle.com
To:     Gerd Rausch <gerd.rausch@...cle.com>, netdev@...r.kernel.org
Cc:     David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next 3/7] net/rds: Wait for the FRMR_IS_FREE (or
 FRMR_IS_STALE) transition after posting IB_WR_LOCAL_INV

On 7/1/19 1:55 PM, Gerd Rausch wrote:
> Hi Santosh,
> 
> On 01/07/2019 13.41, santosh.shilimkar@...cle.com wrote:
>>> @@ -144,7 +146,29 @@ static int rds_ib_post_reg_frmr(struct rds_ib_mr *ibmr)
>>>            if (printk_ratelimit())
>>>                pr_warn("RDS/IB: %s returned error(%d)\n",
>>>                    __func__, ret);
>>> +        goto out;
>>> +    }
>>> +
>>> +    if (!frmr->fr_reg)
>>> +        goto out;
>>> +
>>> +    /* Wait for the registration to complete in order to prevent an invalid
>>> +     * access error resulting from a race between the memory region already
>>> +     * being accessed while registration is still pending.
>>> +     */
>>> +    wait_event_timeout(frmr->fr_reg_done, !frmr->fr_reg,
>>> +               msecs_to_jiffies(100));
>>> +
>> This arbitrary timeout in this patch as well as pacth 1/7 which
>> Dave pointed out has any logic ?
>>
> 
> It's empirical (see my response to David's question):
> Memory registrations took longer than invalidations, hence 100msec instead of 10msec.
> 
>> MR registration command issued to hardware can at times take as
>> much as command timeout(e.g 60 seconds in CX3) and upto that its still
>> legitimate operation and not necessary failure. We shouldn't add
>> arbitrary time outs in ULPs.
> 
> Where did you find the 60 seconds for CX3 you are referring to?
> Is there a "generic" upper-bound that is not tied to a specific vendor / HCA?
> Can you provide a pointer?
> 
Look for command timeout in CX3 sources. 60 second is upper bound in
CX3. Its not standard in specs(at least not that I know) though
and may vary from vendor to vendor.

Regards,
Santosh