Date: Tue, 19 Jan 2016 00:41:43 +0100 From: Marius Strobl <marius@alchemy.franken.de> To: Kubilay Kocak <koobs@FreeBSD.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r293854 - head/sys/dev/e1000 Message-ID: <20160118234142.GM15359@alchemy.franken.de> In-Reply-To: <5698473F.8030203@FreeBSD.org> References: <201601132147.u0DLlR38017711@repo.freebsd.org> <5698473F.8030203@FreeBSD.org>
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On Fri, Jan 15, 2016 at 12:11:27PM +1100, Kubilay Kocak wrote: > On 14/01/2016 8:47 AM, Marius Strobl wrote: > > Author: marius > > Date: Wed Jan 13 21:47:27 2016 > > New Revision: 293854 > > URL: https://svnweb.freebsd.org/changeset/base/293854 > > > > Log: > > Given that em(4), lem(4) and igb(4) hardware doesn't require the > > alignment guarantees provided by m_defrag(9), use m_collapse(9) > > instead for performance reasons. > > While at it, sanitize the statistics softc members, i. e. retire > > unused ones and add SYSCTL nodes missing for actually used ones. > > > > Differential Revision: https://reviews.freebsd.org/D4717 > > > > Modified: > > head/sys/dev/e1000/if_em.c > > head/sys/dev/e1000/if_em.h > > head/sys/dev/e1000/if_igb.c > > head/sys/dev/e1000/if_igb.h > > head/sys/dev/e1000/if_lem.c > > head/sys/dev/e1000/if_lem.h > > What kind of performance / overhead delta can be expected for this change? > Compared to m_collapse(9), m_defrag(9) is a real CPU hog. However, bus_dmamap_load_mbuf_sg(9) should fail seldom enough with EFBIG that you'll most likely not experience much of a difference in practice. Still, unnecessary use of m_defrag(9) in place of m_collapse(9) should be avoided and at some point in time we actually had managed to get rid of most of these cases. Unfortunately, such code came back in a couple of drivers, mainly in vendor-supplied ones. > Is this worth MFC and/or Relnotes ? The change is worth an MFC but not Relnotes. Marius
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