Date: Tue, 06 Nov 2012 12:42:53 +0100 From: Andre Oppermann <andre@freebsd.org> To: Fabien Thomas <fabien.thomas@netasq.com> Cc: Davide Italiano <davide@freebsd.org>, Luigi Rizzo <rizzo@iet.unipi.it>, Joe Holden <lists@rewt.org.uk>, Ryan Stone <rysto32@gmail.com>, FreeBSD Current <current@freebsd.org> Subject: Re: polling's future [was: Re: Dynamic Ticks/HZ] Message-ID: <5098F7BD.9060204@freebsd.org> In-Reply-To: <04A8DD03-71B2-4EFA-864B-522F49BF1478@netasq.com> References: <509758B8.1000409@rewt.org.uk> <CACYV=-HwJ1j2-zDtCtuGNKzdFRJhPsZm6vtFXAVyPSabCXvFEQ@mail.gmail.com> <50975F6F.6010907@rewt.org.uk> <CACYV=-Ef5ij7%2BgqDV9oS3xRyD6Yy2mqDyKqqUZZQ-KsWb_3C3A@mail.gmail.com> <5097898C.9080109@rewt.org.uk> <CAFMmRNwR_XxjnRZvxqew77qNnOTGWrRQnhJkg4u2berL8VCVtw@mail.gmail.com> <20121105163654.GA12870@onelab2.iet.unipi.it> <5097E880.8010001@rewt.org.uk> <20121105165748.GA13098@onelab2.iet.unipi.it> <5098E526.6070101@freebsd.org> <04A8DD03-71B2-4EFA-864B-522F49BF1478@netasq.com>
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On 06.11.2012 12:02, Fabien Thomas wrote: >>> >> >> Hi Luigi, >> >> do you agree on polling having outlived its usefulness in the light >> of interrupt moderating NIC's and SMP complications/disadvantages? >> > If you have only one interface yes polling is not really necessary. > > If you have 10 interfaces the interrupt moderation threshold is hard to find > to not saturate the system. > Doing polling at 8000hz in that case is a lot better regarding global interrupt level. OK. Is the problem the interrupt load itself, or the taskqueues? > The problem is that in the current state polling does not work well and people remember > the good old time where polling was better. Indeed. > rstone@ and myself have made some improvement to polling. > > You can find a diff here for 8.3 with updated intel driver : > http://people.freebsd.org/~fabient/polling/patch-pollif_8.3_11052012 > > - support multiqueue for ixgbe, igb, em. > - compat API for old driver > - keep interrupt for link / status > - user core mapping / auto mapping > - deadline to keep cpu available > - integrated to netisr > - deferred packet injection with optional prefetching This is a number of interesting but sometimes only tangentially related features. Lets focus on the network cpu monopolization issue first. > Performance are on par with interrupt but you can keep a system alive more easily > by accounting all network processing for the deadline (with direct dispatch). Would you be willing to work a solution with me with a load aware taskqueue as I proposed in a recent email to Luigi? That way we don't need special cases or features or even a normal server under DDoS wouldn't go down. -- Andre
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