Date: Tue, 24 Oct 2006 10:13:05 +0100 From: Karl Pielorz <kpielorz@tdx.co.uk> To: Robert Watson <rwatson@FreeBSD.org> Cc: Kostik Belousov <kostikbel@gmail.com>, freebsd-hackers@freebsd.org Subject: Re: 6.1-STABLE hangs, ddb shows 'acpi_timer_read'? Message-ID: <A654F4C5C2A9196BEDC14E6E@quadro.tdx.co.uk> In-Reply-To: <20061020134552.H38852@fledge.watson.org> References: <D5A35FC423766495F2B3D855@Unsupported> <20061020110151.GU55428@deviant.kiev.zoral.com.ua> <82C14B40C9061504218D7585@Unsupported> <20061020134552.H38852@fledge.watson.org>
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--On 20 October 2006 13:47 +0100 Robert Watson <rwatson@FreeBSD.org> wrote: >> I'm just a little hesitant to put it all in, and end up with a machine >> that's 80% slower :( > > Depends a lot on your workload. WITNESS used to really, really slow > things down for kernel lock intensive workloads (VFS especially); now it > just really slows things down. INVARIANTS overhead is generally > measurable, but for most workloads it is likely <20%. The place > INVARIANTS hits you is when the kernel is allocating and freeing lots of > memory, during which INVARIANTS will be scrubbing and checking for use > after free, etc. It's worth running with WITNESS when debugging > deadlocks if possible, because it is, essentially, a deadlock debugging > tool. A moderate number of people run with INVARIANTS in production, but > you generally don't want to do that with WITNESS. Well this is happening on an almost daily basis for me, so I threw everything in. I'd rather have lousy performance for a couple of days - and get all the info needed to fix the problem, than fsck a terrabyte, and mop up after a hung machine daily ;) Thanks for the replies, crossing fingers now :) -Karl
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