Re: network performance, a low-level measurement

From: Poul-Henning Kamp (phk_at_phk.freebsd.dk)
Date: 01/31/05

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    To: Robert Watson <rwatson@FreeBSD.org>
Date: Mon, 31 Jan 2005 13:35:15 +0100

    In message <Pine.NEB.3.96L.1050131112831.35704A-100000@fledge.watson.org>, Robert Watson writes:

    >What about INVARIANTS? That causes an extra mutex grab and release on
    >each allocation and free, so INVARIANTS should be disabled in any
    >performance-sensitive or timing-sensitive measurements.

    new test starting in a moment.

    >> o unshared interrupt line
    >> o if_sis driver modified to FAST intr which just schedules
    >> the existing sis_intr on taskqueue_fast
    >> o single-user mode
    >> o A back-to-back cable to another machine.
    >> o A single default sized ping packet
    >>
    >>
    >> Time [uSec] Where
    >> -----------------------------------------------------------------------
    >> 000.000 HW-intr start
    >> 011.600 HW-intr stop
    >
    >So this is the time window from the edge of the interrupt being raised, to
    >it being lowered as a result of ACK'ing the hardware, or what exactly?

    yes, this is the measured width of the signal on the physical interrupt
    wire running from the chip.

    >it being lowered as a result of ACK'ing the hardware, or what exactly? Do
    >you have any timing related to when the low level interrupt code enters,
    >the fast handler starts running, when it stops running, and when the low
    >level code returns (followed shortly by preemption)?

    Hmm, I can do that I think.

    >> 067.200 Enter sis_intr_task()
    >> 074.000 Enter sis_rxeof()
    >> 134.800 Enter ifp->if_input()
    >> 552.800 Enter sis_startl()
    >
    >Is net.isr.enable=1 or net.isr.enable=0?

    Whatever the default is.

    >Why are we entering sis_start()
    >here if net.isr.enable=0 and the system is otherwise idle?

    sis_start is called to return the ICMP ECHO reply packet obviously :-) 

    -- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.
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