On 1/10/22 13:45, Peter Zijlstra wrote:
On Mon, Jan 10, 2022 at 11:18:27AM -0500, Waiman Long wrote:
On 1/10/22 03:05, Christoph Hellwig wrote:
Adding the locking primitive maintainers to this patch adding open coded
locking primitives..
On Sat, Jan 08, 2022 at 08:46:17AM -0800, Jaegeuk Kim wrote:
From: Tim Murray <[email protected]>
f2fs rw_semaphores work better if writers can starve readers,
especially for the checkpoint thread, because writers are strictly
more important than reader threads. This prevents significant priority
inversion between low-priority readers that blocked while trying to
acquire the read lock and a second acquisition of the write lock that
might be blocking high priority work.
Signed-off-by: Tim Murray <[email protected]>
Signed-off-by: Jaegeuk Kim <[email protected]>
We could certainly implement a down_read() variant (e.g.
down_read_lowprio()) with its own slowpath function to do this within the
rwsem code as long as there is a good use-case for this kind of
functionality.
I think _unfair() or something along those lines is a *much* better
naming that _lowprio(). Consider a RT task ending up calling _lowprio().
That just doesn't make conceptual sense.
I am fine with the _unfair() name as I am not good at naming:-)
And then there's the lockdep angle; the thing being unfair will lead to
scenarios where lockdep will give a false positive because it expects
the r-w-r order to block things, which won't happen. A position needs to
be taken a-prioriy.
Right, we may need to twist lockdep to match the new behavior if we are
going to provide such a functionality.
Cheers,
Longman
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