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Date:      Tue, 17 Sep 2013 12:28:41 -0600
From:      Ian Lepore <ian@FreeBSD.org>
To:        Harald Schmalzbauer <h.schmalzbauer@omnilan.de>
Cc:        lev@FreeBSD.org, FreeBSD Stable <freebsd-stable@FreeBSD.org>, freebsd-usb@FreeBSD.org, Hans Petter Selasky <hans.petter.selasky@bitfrost.no>
Subject:   Re: umcs (4-Port-USB-serial) triggering way too much ehci IRQs
Message-ID:  <1379442521.1197.50.camel@revolution.hippie.lan>
In-Reply-To: <52389248.7080109@omnilan.de>
References:  <52372DBA.6020703@omnilan.de> <zarafa.5237e529.2bc6.08fde6eb34c27a87@mail.lockless.no> <875323075.20130917124437@serebryakov.spb.ru> <523816E1.10603@omnilan.de> <1857258551.20130917124737@serebryakov.spb.ru> <5238198C.3070604@bitfrost.no> <52381BAC.5010801@omnilan.de> <52381FCA.5030509@bitfrost.no> <5238775C.8010000@omnilan.de> <1379434567.1197.48.camel@revolution.hippie.lan> <52389248.7080109@omnilan.de>

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On Tue, 2013-09-17 at 19:32 +0200, Harald Schmalzbauer wrote:
> Bez=FCglich Ian Lepore's Nachricht vom 17.09.2013 18:16 (localtime):
> > On Tue, 2013-09-17 at 17:38 +0200, Harald Schmalzbauer wrote:
> >> ...
> >>> Try this patch and see what happens:
> >>>
> >>> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> >>> --- umcs.c    (revision 255492)
> >>> +++ umcs.c    (local)
> >>> @@ -230,6 +230,7 @@
> >>>          .bufsize =3D 0,        /* use wMaxPacketSize */
> >>>          .callback =3D &umcs7840_intr_callback,
> >>>          .if_index =3D 0,
> >>> +        .interval =3D 20, /* ms */
> >>>      },
> >>>  };
> >>>
> >>>
> >>> BTW: I see that the umcs driver shouldn't do synchronous control
> >>> transfers from the USB interrupt transfer callback. This should be
> >>> postponed into some worker thread, for example the USB explore thre=
ad.
> >>> See USB audio driver for an example.
> >>>
> >>> --HPS
> >> I tried your patch and it works as expected: IRQs decreased to ~64/s
> >> when idle/disconnected.
> >>
> >> One interesting thing I never measured before:
> >> Console connection with 115k2 via umcs and 'while ( 2>1 ) echo "---.=
.."
> >> end' results in 8000 irqs/s :-( But that's also true for the prolifi=
c
> >> (uplcom). The latter just goes down to 0.0 irqs/s when idle.
> >>
> >> Doing the same with uart0 results in 1444irqs/s.
> >> Is it by design/unavoidable that transfering the same via USB multip=
lies
> >> by factor 5-6?
> >>
> >> Thanks,
> >>
> >> -Harry
> >>
> > I don't know about that chipset, but with the FTDI chips it does xfer=
s
> > in 64 byte chunks and high speed bulk data results in an astronomical
> > number of interrupts (and if you go fast enough, lost data).  I have
>=20
> According to ASIX product brief, MCS7840 has 512 byte buffer. Pretty
> much for an UART I think, which should make 115k2 baud connections  wit=
h
> less than 30 transfers/s work, or am I missing something?

That's the internal buffer, it still does usb transfers in smaller
chunks.  Some ftdi chips have 4k onboard buffers but do 64-byte usb
transfers.

-- Ian





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