Date: Thu, 13 Dec 2012 15:05:00 +0200 From: Andriy Gapon <avg@FreeBSD.org> To: vbox@FreeBSD.org, freebsd-emulation@FreeBSD.org Subject: issue with under-tick waits Message-ID: <50C9D27C.1090707@FreeBSD.org>
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I think that the following patch is needed in VirtualBox 4.2.4 kernel module:
--- sleepqueue-r0drv-freebsd.h.orig 2012-12-12 20:09:29.675203802 +0200
+++ sleepqueue-r0drv-freebsd.h 2012-12-12 20:11:53.604203131 +0200
@@ -82,6 +82,8 @@
uint64_t cTicks = ASMMultU64ByU32DivByU32(uTimeout, hz, UINT32_C(1000000000));
if (cTicks >= INT_MAX)
return RTSEMWAIT_FLAGS_INDEFINITE;
+ else if (cTicks == 0 && uTimeout > 0)
+ pWait->iTimeout = 1;
else
pWait->iTimeout = (int)cTicks;
#endif
Without this patch any waits for periods shorter than a single tick return
immediately leading to a lot of unnecessary spinning. For example, I observe that
my guest's idle loop does a lot of sleeps with periods slightly shorter than 1 ms
(1/hz), e.g. 900us. All that waiting turns into pure spinning and VirtualBox eats
100% of a core.
The above patch improves the situation significantly. Also, it (approximately)
follows what tvtohz does.
--
Andriy Gapon
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