|| ||Linus Torvalds <torvalds-AT-osdl.org>|
|| ||Ingo Molnar <mingo-AT-elte.hu>|
|| ||Re: [patch] remove the BKL (Big Kernel Lock), this time for real|
|| ||Wed, 15 Sep 2004 08:40:55 -0700 (PDT)|
|| ||linux-kernel-AT-vger.kernel.org, Andrew Morton <akpm-AT-osdl.org>,
William Lee Irwin III <wli-AT-holomorphy.com>,
Arjan van de Ven <arjanv-AT-redhat.com>, Lee Revell <rlrevell-AT-joe-job.com>|
On Wed, 15 Sep 2004, Ingo Molnar wrote:
> the attached patch is a new approach to get rid of Linux's Big Kernel
> Lock as we know it today.
I really think this is wrong.
Maybe not from a conceptual standpoint, but that implementation with the
scheduler doing "reaquire_kernel_lock()" and doing a down() there is just
wrong, wrong, wrong.
If we're going to do a down() and block immediately after being scheduled,
I don't think we should have been picked in the first place.
Yeah, yeah, you have all that magic to not recurse by setting lock-depth
negative before doing the down(), but it still feels fundamentally wrong
to me. There's also the question whether this actually _helps_ anything,
since it may well just replace the spinning with lots of new scheduler
And you make schedule() a lot more expensive for kernel lock holders by
copying the CPU map. You may have tested it on a machine where the CPU map
is just a single word, but what about the big machines?
Spinlocks really _are_ cheaper. Wouldn't it be nice to just continue
removing kernel lock users and keeping a very _simple_ kernel lock for
In other words, I'd _really_ like to see some serious numbers for this.
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