Re: [PATCH 1/2] locking: Implement an algorithm choice for Wound-Wait mutexes

From: Thomas Hellstrom
Date: Wed Jun 13 2018 - 04:34:45 EST

On 06/13/2018 09:54 AM, Greg Kroah-Hartman wrote:
On Wed, Jun 13, 2018 at 09:47:44AM +0200, Thomas Hellstrom wrote:
+The algorithm (Wait-Die vs Wound-Wait) is chosen using the _is_wait_die
+argument to DEFINE_WW_CLASS(). As a rough rule of thumb, use Wound-Wait iff you
+typically expect the number of simultaneous competing transactions to be small,
+and the rollback cost can be substantial.
Three different ways to acquire locks within the same w/w class. Common
definitions for methods #1 and #2:
-static DEFINE_WW_CLASS(ww_class);
+static DEFINE_WW_CLASS(ww_class, false);
Minor nit on the api here. Having a "flag" is a royal pain. You have
to go and look up exactly what that "true/false" means every time you
run across it in code to figure out what it means. Don't do that if at
all possible.

Make a new api:
instead that then wraps that boolean internally to switch between the
different types. That way the api is "self-documenting" and we all know
what is going on without having to dig through a header file.


greg k-h

Good point. I'll update in a v2.