From: Wolfgang Grandegger <wg@grandegger.com>
To: "Ira W. Snyder" <iws@ovro.caltech.edu>
Cc: linux-can@vger.kernel.org
Subject: Re: [PATCH 0/3] can: janz-ican3: fix support for CAN_RAW_RECV_OWN_MSGS
Date: Tue, 10 Jul 2012 08:09:53 +0200 [thread overview]
Message-ID: <4FFBC731.60408@grandegger.com> (raw)
In-Reply-To: <1341863790-5645-1-git-send-email-iws@ovro.caltech.edu>
Hi Ira,
On 07/09/2012 09:56 PM, Ira W. Snyder wrote:
> From: "Ira W. Snyder" <iws@ovro.caltech.edu>
>
> This is another different approach to fixing the Janz ICAN3 support for
> CAN_RAW_RECV_OWN_MSGS.
>
> The can_put_echo_skb() function is changed to always keep all packets
> until can_get_echo_skb() is called. Previously, it would drop packets if
> they were not needed to be looped back. This makes it possible for the
> new function can_cmp_echo_skb() to work with hardware-assisted loopback
> support on the Janz ICAN3, which does not have TX-complete interrupts of
> any kind.
>
> Since we are now storing packets even in the non-loopback case, there is
> some extra memory overhead, to store the extra packets between the calls
> to can_put_echo_skb() and can_get_echo_skb().
Well, I don't like such device specific quirk going into the common
interface.
> After this patch series is applied, the SocketCAN tst-rcv-own-msgs test
> passes.
>
> Performance is rougly 15% less than using the previously posted patch:
> [PATCH ALTERNATE VERSION 1/1] can: janz-ican3: fix support for CAN_RAW_RECV_OWN_MSGS
Oops, that's a lot and a clear contra.
> This performance drop is due to the extra overhead of receiving the echo
> packets from the card itself. This involves one extra interrupt for each
> packet sent, and the associated overhead of running ican3_napi() for
> each packet sent.
Do we really want that. I agree that CAN_RAW_RECV_OWN_MSGS should work
as expected but we should not try hard to partially fix the timing
issue. Why do we not just use the default protocol callback (flags &=
!IFF_ECHO) if the hardware cannot do it better.
Wolfgang.
next prev parent reply other threads:[~2012-07-10 6:09 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-09 19:56 [PATCH 0/3] can: janz-ican3: fix support for CAN_RAW_RECV_OWN_MSGS Ira W. Snyder
2012-07-09 19:56 ` [PATCH 1/3] can: make the echo stack keep packet information longer Ira W. Snyder
2012-07-09 21:09 ` Oliver Hartkopp
2012-07-09 19:56 ` [PATCH 2/3] can: add can_cmp_echo_skb() for echo skb comparison Ira W. Snyder
2012-07-09 19:56 ` [PATCH 3/3] can: janz-ican3: fix support for CAN_RAW_RECV_OWN_MSGS Ira W. Snyder
2012-07-09 20:57 ` Oliver Hartkopp
2012-07-09 21:16 ` Ira W. Snyder
2012-07-10 6:40 ` Wolfgang Grandegger
2012-07-09 21:05 ` [PATCH 0/3] " Oliver Hartkopp
2012-07-09 21:29 ` Ira W. Snyder
2012-07-10 6:09 ` Wolfgang Grandegger [this message]
2012-07-10 6:59 ` Wolfgang Grandegger
2012-07-10 15:22 ` Ira W. Snyder
2012-07-10 19:19 ` Oliver Hartkopp
2012-07-10 20:34 ` Wolfgang Grandegger
-- strict thread matches above, loose matches on Subject: below --
2012-07-12 16:15 Ira W. Snyder
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