Date: Mon, 25 Feb 2002 12:09:34 +1100 (EST) From: Bruce Evans <bde@zeta.org.au> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Terry Lambert <tlambert2@mindspring.com>, Alfred Perlstein <alfred@FreeBSD.ORG>, Bosko Milekic <bmilekic@unixdaemons.com>, Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp>, <current@FreeBSD.ORG>, John Baldwin <jhb@FreeBSD.ORG> Subject: Re: Success! critical_enter()/critical_exit() revamp (was Re: malloc_bucket() idea (was Re: How to fix malloc.)) Message-ID: <20020225111741.S36145-100000@gamplex.bde.org> In-Reply-To: <200202241109.g1OB9cn68688@apollo.backplane.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Sun, 24 Feb 2002, Matthew Dillon wrote:
> Bruce, your sys.dif was *invaluable*! It would have taken me a lot
> longer to figure out the interrupt disablement requirement around
> the icu_lock, and the statclock and hardclock forwarding issues (which I
> got working by the way!).
Thanks.
> It turns out that putting the pending masks in the per-cpu area was
> the right solution! It made statclock and hardclock forwarding easy
> (I can see why you didn't even try in your patch set, doing it with
> a global mask would be nearly impossible). In fact, it made everything
> unbelievably easy.
> ...
[This paragraph reordered]
> up. One of the best things about this patch set is that it is really
> flexible. We should be able to really make interrupts fly. In fact,
> it should even be possible for one cpu to steal another cpu's pending
> interrupt(s) fairly trivially, without having to resort to IPIs.
Good idea. Stealing would be even easier if the mask were global :-).
> The second issue is that cpu_switch() does not save/restore the
> PSL_I (interrupt disablement mask). I added a PSL word to the PCB
> structure to take care of the problem. Without this if you have
> a thread switch away while holding interrupts hard-disabled, the
> next thread will inherit the hard disablement. I saw the sti's
> you added in various places but I figured the best solution was
> to simply save/restore the state. The original code didn't have
cpu_switch() certainly needs to do this if it can be called with the
interrupt enable flag[s] in different states. I need the sti's (actually
enable_intr()'s because I don't want fast interrupts to be disabled
during context switches. This works because enabling interrupts is sure
to be safe, since we might be switching to a thread that will enable
them. Some sort of lock is needed to prevent interrupts interfering
with the switch. I think soft-masking them in critical_enter() is
sufficient in your version too.
Bruce
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20020225111741.S36145-100000>