Date: Tue, 6 Sep 2011 16:44:48 -0600 From: Manish Vachharajani <manishv@lineratesystems.com> To: Alexander Best <arundel@freebsd.org> Cc: freebsd-hackers@freebsd.org Subject: Re: excessive use of gettimeofday(2) and other syscalls Message-ID: <CAHRgBhRe8n%2BV3nSzRn4_fctHB1nie2ACk7oRVOPJqqKaMUgKrg@mail.gmail.com> In-Reply-To: <20110906220115.GA25048@freebsd.org> References: <20110906220115.GA25048@freebsd.org>
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Under 7.3 (haven't checked 8 or 9) this issue crops up because the time system call calls gettimeofday under the hood (see lib/libc/gen/time.c). As a result, the kernel tries to get an accurate subsecond resolution time that simply gets chopped to the nearest second. Lots of libraries assume that time is fast because it is fast under Linux. Every instance where I have seen this as a performance issue, the call has been to time not a direct call to gettimeofday. The latest openssl (not the one from FreeBSD, but the one from openssl.org has this issue for example. Manish On Tue, Sep 6, 2011 at 4:01 PM, Alexander Best <arundel@freebsd.org> wrote: > hi there, > > in a recent discussion on current@ [1], it was discovered that chromium makes > excessive use of gettimeofday(2). while searching google, i found other > software that is/was having the same issue [2]. although this is a programming > error, it would still be nice, if freebsd could issue a warning in cases like > these. would it be possible to instruct freebsd to issue a warning, when a > process issues a certain amount of syscalls per second (maybe tuneable via > sysctl)? > > while calling gettimeofday(2) excessively isn't causing any harm, it triggers > a lot of context switches and reduces performance. having such warnings in > place could help a user identify such a process without having to use debugging > tools, such as ktrace or dtrace. > > cheers. > alex > > [1] http://www.mail-archive.com/freebsd-current@freebsd.org/msg131040.html > [1] https://forum.transmissionbt.com/viewtopic.php?f=2&t=11687 > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org" > -- Manish Vachharajani Founder LineRate Systems manishv@lineratesystems.com (609)635-9531 M
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