[antinvidia@gmail.com: some questions about bge(4)]

[Oleg Bulyzhin]

On Thu, Dec 14, 2006 at 12:55:51AM +0000, MQ wrote:
> 2006/12/12, Oleg Bulyzhin <oleg at freebsd.org>:
> >
> >On Wed, Dec 06, 2006 at 11:54:01AM +0300, Gleb Smirnoff wrote:
> >>   Forwarding to net@ list and to Oleg, who has made polling
> >> support for bge(4).
> >>
> >> ----- Forwarded message from MQ < antinvidia at gmail.com> -----
> >>
> >> From: MQ <antinvidia at gmail.com>
> >> To: glebius at freebsd.org, davidch at broadcom.com
> >> Subject: some questions about bge(4)
> >> Date: Sat, 2 Dec 2006 09:32:27 +0000
> >> Delivered-To: glebius at freebsd.org
> >> DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws;
> >>         s=beta; d=gmail.com;
> >>
> >h=received:message-id:date:from:to:subject:mime-version:content-type;
> >>
> >b=ZL3ZZ1zR0mt4LaUN2Rr+jXTPSzQgJYRwLiwKnv95r2UCEids5Wl7oA2BNgicJ2QRG8OalJ7DqY7lM1HBgv0OVTlXOhGQ9aFmKQAuTNi6ueZA817XUacXyViEepnj0oNyYgAnkbaaBO1+nl2Fpb3IxV+MIe575WRlqbglF8kdOek=
> >
> >>
> >> Hi David and Gleb,
> >>    I'm using several chips whose driver is bge(4). And now I have some
> >> questions about the driver, would you please an answer for me?
> >>    My confusion is related with some codes in /sys/dev/mii/brgphy.c. The
> >
> >> bge(4) uses the callout to drive the watchdog. And the brgphy_service()
> >is
> >> called once per second. It calls brgphy_mii_phy_auto() every 5 seconds
> >to
> >> autonegotiate the media. Normally, it costs about 0.5ms in the first
> >> function brgphy_service(), and about 5ms when autonegotiation is
> >proceeded.
> >
> >brgphy_mii_phy_auto() is called only if there is no link.
> >
> >>    I haven't done streestest on it, consequently I don't know if this
> >delay
> >> will cause packets to be dropped. But I've enabled device polling with
> >the
> >> bge(4) on FreeBSD 6.1-RELEASE. If HZ is set to a high value(e.g. 4000),
> >this
> >> delay will cause the kern.polling.lost_polls to increase by one or two
> >every
> >> second. And for about five seconds, the lost poll will increase by at
> >least
> >> 16 regularly. So I think this behavior has some impact on the systems
> >that
> >> enables device polling. Could we get something to make the bge(4) a bit
> >more
> >> friendly to the device polling? I don't know if autonegotiation is
> >really
> >> needed to be called so frequently when we are connected to a good
> >network
> >> environment. Can I modify the interval between two autonegotiations to
> >have
> >> less lost_polls? However, I have no idea about the long time spent in
> >the
> >> brgphy_service(), please take a look at the problem when you have enough
> >> time.
> >
> >If you have lost poll it does not guarantee packet loss.
> >Packets can be retrieved by next poll or even by idle_poll thread.
> >bge_tick() is doing couple of pci register reads (it's polling phy status
> >and
> >updates some statistic counters), this why it takes some time.
> >
> >Anyway, you are right about too short autonegotiation timer, i'll fix it
> >soon.
> >
> >>
> >> Regards
> >> MQ
> >>
> >> ----- End forwarded message -----
> >>
> >> --
> >> Totus tuus, Glebius.
> >> GLEBIUS-RIPN GLEB-RIPE
> >
> >--
> >Oleg.
> >
> >================================================================
> >=== Oleg Bulyzhin -- OBUL-RIPN -- OBUL-RIPE -- oleg at rinet.ru ===
> >================================================================
> >
> >
> 
> Oh, I didn't connect to switch in my previous testings, so I didn't notice
> that the brgphy_mii_phy_auto() is called only there is no link. It's my
> fault. Therefore there won't be a problem with this.
> 
> By the way, bge_tick() takes about 0.5ms to finish its work, this results
> the lost poll every second when HZ is higher. Lower HZ will limit the
> performance under heavy traffic, and may result packet loss in that
> situation. And higher HZ will make a confusing situation that whether we
> have encountered a packet loss? It's really hard to make a decision between
> these two kinds of situation.

IMO, high HZ would not give perfomance gain if you have idle polling on
(sysctl kern.polling.idle_poll=1).
So it's better to have HZ=1000 & idle polling, than HZ=10000 and idle polling
disabled.

-- 
Oleg.

================================================================
=== Oleg Bulyzhin -- OBUL-RIPN -- OBUL-RIPE -- oleg at rinet.ru ===
================================================================