Date: Mon, 17 Aug 2015 17:44:37 +0200 From: Alban Hertroys <haramrae@gmail.com> To: Slawa Olhovchenkov <slw@zxy.spb.ru> Cc: Daniel Braniss <danny@cs.huji.ac.il>, FreeBSD Net <freebsd-net@freebsd.org>, FreeBSD stable <freebsd-stable@freebsd.org> Subject: Re: ix(intel) vs mlxen(mellanox) 10Gb performance Message-ID: <CAF-3MvOzNYS_YuawpbM118=pOn8kgFW0EsUzsL5p_1nXXeBgXA@mail.gmail.com> In-Reply-To: <20150817115405.GL1872@zxy.spb.ru> References: <1D52028A-B39F-4F9B-BD38-CB1D73BF5D56@cs.huji.ac.il> <20150817094145.GB3158@zxy.spb.ru> <197995E2-0C11-43A2-AB30-FBB0FB8CE2C5@cs.huji.ac.il> <20150817113923.GK1872@zxy.spb.ru> <CAF-3MvM8-%2BKxP3xr4vF2=c7o4vqCRdPkzQWjHLECzf3Jx8sqxw@mail.gmail.com> <20150817115405.GL1872@zxy.spb.ru>
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On 17 August 2015 at 13:54, Slawa Olhovchenkov <slw@zxy.spb.ru> wrote: > On Mon, Aug 17, 2015 at 01:49:27PM +0200, Alban Hertroys wrote: > >> On 17 August 2015 at 13:39, Slawa Olhovchenkov <slw@zxy.spb.ru> wrote: >> >> > In any case, for 10Gb expect about 1200MGB/s. >> >> Your usage of units is confusing. Above you claim you expect 1200 > > I am use as topic starter and expect MeGaBytes per second That's a highly unusual way of writing MB/s. There are standards for unit prefixes: k means kilo, M means Mega, G means Giga, etc. See: https://en.wikipedia.org/wiki/International_System_of_Units#Prefixes >> million gigabytes per second, or 1.2 * 10^18 Bytes/s. I don't think >> any known network interface can do that, including highly experimental >> ones. >> >> I suspect you intended to claim that you expect 1.2GB/s (Gigabytes per >> second) over that 10Gb/s (Gigabits per second) network. >> That's still on the high side of what's possible. On TCP/IP there is >> some TCP overhead, so 1.0 GB/s is probably more realistic. > > TCP give 5-7% overhead (include retrasmits). > 10^9/8*0.97 = 1.2125 In information science, Bytes are counted in multiples of 2, not 10. A kb is 1024 bits or 2^10 b. So 10 Gb is 10 * 2^30 bits. It's also not unusual to be more specific about that 2-base and use kib, Mib and Gib instead. Apparently you didn't know that... Also, if you take 5% off, you are left with (0.95 * 10 * 2^30) / 8 = 1.1875 B/s, not 0.97 * ... Your calculations were a bit optimistic. Now I have to admit I'm used to use a factor of 10 to convert from b/s to B/s (that's 20%!), but that's probably no longer correct, what with jumbo frames and all. -- If you can't see the forest for the trees, Cut the trees and you'll see there is no forest.
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