Date: Wed, 19 Jul 2006 07:49:59 GMT From: Arthur Hartwig <arthur.hartwig@nokia.com> To: freebsd-gnats-submit@FreeBSD.org Subject: kern/100519: Suboptimal network polling Message-ID: <200607190749.k6J7nxK5023181@www.freebsd.org> Resent-Message-ID: <200607190800.k6J80Zfp023492@freefall.freebsd.org>
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>Number: 100519
>Category: kern
>Synopsis: Suboptimal network polling
>Confidential: no
>Severity: non-critical
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Wed Jul 19 08:00:34 GMT 2006
>Closed-Date:
>Last-Modified:
>Originator: Arthur Hartwig
>Release: 6.0
>Organization:
Nokia
>Environment:
FreeBSD xxx.nokia.com 6.0-RELEASE FreeBSD 6.0-RELEASE #3: Wed Mar 1 10:46:02 EST 2006 hartwig@xxx.nokia.com:/usr/src/sys/i386/compile/oz-net-10 i386
>Description:
Network polling has unnecessary calls to the scheduler. These require acquiring the sched lock which imposes a variable delay depending on contention for this lock.
in netisr_pollmore() in kern/kern_poll.c there are two calls to schednetisrbits(). schednetisrbits is defined in net/netisr.h to set some bits in netisr and call legacy_setsoftnet(). legacy_setsoftnet() in net/netisr.c calls swi_sched(). swi_sched() in kern/kern_intr.c which calls ithread_schedule() in the same file. ithread_schedule() acquires and releases the sched_lock.
>How-To-Repeat:
>Fix:
Since the netisr is running when netisr_pollmore() is executing and swi_net() the main netisr despatcher loops until netisr is zero, it is sufficient in netisr_pollmore() to just set the bits in netisr and not also call legacy_setsoftnet():
replace the two instances of:
schednetisrbits(1 << NETISR_POLL | 1 << NETISR_POLLMORE);
in netisr_pollmore() by:
atomic_set_rel_int(&netisr, (1 << NETISR_POLL | 1 << NETISR_POLLMORE));
>Release-Note:
>Audit-Trail:
>Unformatted:
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