svn commit: r293439 - in head: lib/libc/sys sys/dev/ti sys/kern sys/sys usr.bin/netstat
NGie Cooper
yaneurabeya at gmail.com
Fri Jan 8 21:22:49 UTC 2016
> On Jan 8, 2016, at 13:10, Gleb Smirnoff <glebius at FreeBSD.org> wrote:
>
> On Fri, Jan 08, 2016 at 12:44:32PM -0800, NGie Cooper wrote:
> N> > Log:
> N> > New sendfile(2) syscall. A joint effort of NGINX and Netflix from 2013 and
> N> > up to now.
> N> >
> N> > The new sendfile is the code that Netflix uses to send their multiple tens
> N> > of gigabits of data per second. The new implementation features asynchronous
> N> > I/O, when I/O operations are launched, but not awaited to be complete. An
> N> > explanation of why such behavior is beneficial compared to old one is
> N> > going to be too long for a commit message, so we will skip it here.
> N> >
> N> > Additional features of new syscall are extra flags, which provide an
> N> > application more control over data sent. The SF_NOCACHE flag tells
> N> > kernel that data shouldn't be cached after it was sent. The SF_READAHEAD()
> N> > macro allows to specify readahead size in pages.
> N> >
> N> > The new syscalls is a drop in replacement. No modifications are required
> N> > to applications. One can take nginx binary for stable/10 and run it
> N> > successfully on head. Although SF_NODISKIO lost its original sense, as now
> N> > sendfile doesn't block, and now means something completely different (tm),
> N> > using the new sendfile the old way is absolutely safe.
> N> >
> N> > Celebrates: Netflix global launch!
> N> > Sponsored by: Nginx, Inc.
> N> > Sponsored by: Netflix
> N> > Relnotes: yes
> N>
> N> Did anyone review these changes and the other changes made recently to sys/kern and sys/net* ?
>
> 1) The review requests were sent continuosly to arch@ during last 1.5 years.
>
> https://lists.freebsd.org/pipermail/freebsd-arch/2014-May/015385.html
>
> 2) Team of engineers at Netflix has a lot of code build on top of that code,
> e.g. SSL_sendfile(). Of course, writing something on top assumes reviewing,
> so assume it reviewed thoroughly by rrs at . Actually, here is list of people
> who did some review of the code: emax@, rrs@, scottl@, gallatin@, imp at .
>
> 3) Do you have any particulars concerns with this change or those made recently
> to sys/kern and sys/net*?
I don’t as of right now, other than it’s really difficult to audit changes and assess risk if someone doesn’t have access to the CRs :(.
Also…
N> > An
N> > explanation of why such behavior is beneficial compared to old one is
N> > going to be too long for a commit message, so we will skip it here.
This wasn’t really helpful. It would have been nice if there was a wiki page or some other reference used in this commit which would have described the where, why, and how behind this change a lot more.
Thanks,
-NGie
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