From: Julian Wiedmann <jwi@linux.ibm.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: David Miller <davem@davemloft.net>,
netdev <netdev@vger.kernel.org>,
linux-s390 <linux-s390@vger.kernel.org>,
Heiko Carstens <hca@linux.ibm.com>,
Ursula Braun <ubraun@linux.ibm.com>,
Karsten Graul <kgraul@linux.ibm.com>
Subject: Re: [PATCH net-next 4/4] s390/qeth: use all configured RX buffers
Date: Fri, 31 Jul 2020 09:50:43 +0200 [thread overview]
Message-ID: <dcc95391-0dea-e7d4-1901-25c00c7a3c60@linux.ibm.com> (raw)
In-Reply-To: <20200730163714.7d6a5017@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
On 31.07.20 01:37, Jakub Kicinski wrote:
> On Thu, 30 Jul 2020 17:01:21 +0200 Julian Wiedmann wrote:
>> The (misplaced) comment doesn't make any sense, enforcing an
>> uninitialized RX buffer won't help with IRQ reduction.
>>
>> So make the best use of all available RX buffers.
>
> Often one entry in the ring is left free to make it easy to
> differentiate between empty and full conditions.
>
> Is this not the reason here?
>
Hmm no, the HW architecture works slightly different.
There's no index register that we could query for HW progress,
each ring entry has an associated state byte that needs to be
inspected and indicates HW progress (among other things).
So this was more likely just a mis-interpretation of how the
(quirky) IRQ reduction mechanism works in HW, or maybe part of
a code path that got removed during the NAPI conversion.
next prev parent reply other threads:[~2020-07-31 7:50 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-30 15:01 [PATCH net-next 0/4] s390/qeth: updates 2020-07-30 Julian Wiedmann
2020-07-30 15:01 ` [PATCH net-next 1/4] s390/qeth: tolerate pre-filled RX buffer Julian Wiedmann
2020-07-30 15:01 ` [PATCH net-next 2/4] s390/qeth: integrate RX refill worker with NAPI Julian Wiedmann
2020-07-30 15:01 ` [PATCH net-next 3/4] s390/qeth: don't process empty bridge port events Julian Wiedmann
2020-07-30 15:01 ` [PATCH net-next 4/4] s390/qeth: use all configured RX buffers Julian Wiedmann
2020-07-30 23:37 ` Jakub Kicinski
2020-07-31 7:50 ` Julian Wiedmann [this message]
2020-07-30 23:39 ` [PATCH net-next 0/4] s390/qeth: updates 2020-07-30 Jakub Kicinski
2020-07-31 23:44 ` David Miller
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