Question about rr alternative design

Kyle Huey me at kylehuey.com
Tue Feb 20 19:44:13 UTC 2018


On Wed, Feb 21, 2018 at 8:14 AM, Octav Chipara <ochipara at gmail.com> wrote:
> Hi,
>
> I have a question about the mechanisms that rr uses the record sys calls. One of the issues that limits rr's performance is that intercepting system calls usually requires 2 context switches (without the Seccomp optimization) . An alternative would be to intercept/wrap libc calls that map to system calls and perform most of the logging in user space. I was wondering if you guys took a look at this alternative.
>
> Thanks,
> — Octav
> _______________________________________________
> rr-dev mailing list
> rr-dev at mozilla.org
> https://mail.mozilla.org/listinfo/rr-dev

There are a number of reasons to record at the syscall boundary rather
than the libc boundary, the most fundamental of which is that nothing
requires a program to use libc. Software can always choose to make
syscalls directly.

If you are seeing your recording performance suffering from a large
number of context switches on simple syscalls you should identify the
syscalls so we can try to buffer them.

- Kyle


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