From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Anna-Maria Behnsen <anna-maria@linutronix.de>,
Frederic Weisbecker <frederic@kernel.org>,
Benjamin Segall <bsegall@google.com>,
Eric Dumazet <edumazet@google.com>,
Andrey Vagin <avagin@openvz.org>,
Pavel Tikhomirov <ptikhomirov@virtuozzo.com>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [patch V2 10/17] posix-timers: Make signal_struct::next_posix_timer_id an atomic_t
Date: Wed, 5 Mar 2025 11:28:18 +0300 [thread overview]
Message-ID: <Z8gLIne1nDPa1yp3@grain> (raw)
In-Reply-To: <87ikoo53xy.ffs@tglx>
On Wed, Mar 05, 2025 at 08:31:21AM +0100, Thomas Gleixner wrote:
...
>
> The traversal does not RMW the timer itself, it unmangles the signal
> pointer for comparison in posix_timer_hashed(). posix_timer_by_id() does
> straight comparisons. So both only read.
No, I mean that we read the value then allocate a temp value with 0 bit
excluded implicitly, so it is not a straight read, but whatever.
> Sure, we can mangle timer ID instead of the signal pointer, but the
> outcome is pretty much the same. The only difference is in
> posix_timer_hashed(), which must detect a taken timer ID independent of
> the timers valid state to prevent collisions.
Bah, I managed to miss that we need to lookup for not yet fully initialized
timers as well, and indeed it makes no much difference which exactly field
to mangle. Thanks a huge for explanations, Thomas!
Cyrill
next prev parent reply other threads:[~2025-03-05 8:28 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-02 19:36 [patch V2 00/17] posix-timers: Rework the global hash table and provide a sane mechanism for CRIU Thomas Gleixner
2025-03-02 19:36 ` [patch V2 01/17] posix-timers: Initialise timer before adding it to the hash table Thomas Gleixner
2025-03-05 17:25 ` Frederic Weisbecker
2025-03-06 8:10 ` Thomas Gleixner
2025-03-06 8:47 ` Frederic Weisbecker
2025-03-07 13:46 ` Frederic Weisbecker
2025-03-02 19:36 ` [patch V2 02/17] posix-timers: Add cond_resched() to posix_timer_add() search loop Thomas Gleixner
2025-03-05 20:54 ` Frederic Weisbecker
2025-03-02 19:36 ` [patch V2 03/17] posix-timers: Cleanup includes Thomas Gleixner
2025-03-05 20:57 ` Frederic Weisbecker
2025-03-02 19:36 ` [patch V2 04/17] posix-timers: Remove a few paranoid warnings Thomas Gleixner
2025-03-05 22:11 ` Frederic Weisbecker
2025-03-02 19:36 ` [patch V2 05/17] posix-timers: Remove SLAB_PANIC from kmem cache Thomas Gleixner
2025-03-07 14:05 ` Frederic Weisbecker
2025-03-02 19:36 ` [patch V2 06/17] posix-timers: Use guards in a few places Thomas Gleixner
2025-03-07 14:16 ` Frederic Weisbecker
2025-03-02 19:36 ` [patch V2 07/17] posix-timers: Simplify lock/unlock_timer() Thomas Gleixner
2025-03-07 22:16 ` Frederic Weisbecker
2025-03-02 19:36 ` [patch V2 08/17] posix-timers: Rework timer removal Thomas Gleixner
2025-03-04 10:10 ` Pavel Tikhomirov
2025-03-04 10:20 ` Pavel Tikhomirov
2025-03-04 14:06 ` Thomas Gleixner
2025-03-07 23:03 ` Frederic Weisbecker
2025-03-08 8:34 ` Thomas Gleixner
2025-03-08 22:48 ` Frederic Weisbecker
2025-03-09 8:21 ` Thomas Gleixner
2025-03-02 19:36 ` [patch V2 09/17] posix-timers: Make lock_timer() use guard() Thomas Gleixner
2025-03-04 14:08 ` [patch V2a " Thomas Gleixner
2025-03-02 19:36 ` [patch V2 10/17] posix-timers: Make signal_struct::next_posix_timer_id an atomic_t Thomas Gleixner
2025-03-03 20:21 ` Cyrill Gorcunov
2025-03-03 21:24 ` Thomas Gleixner
2025-03-04 17:56 ` Cyrill Gorcunov
2025-03-04 20:30 ` Thomas Gleixner
2025-03-04 22:16 ` Cyrill Gorcunov
2025-03-05 7:31 ` Thomas Gleixner
2025-03-05 8:28 ` Cyrill Gorcunov [this message]
2025-03-02 19:37 ` [patch V2 11/17] posix-timers: Improve hash table performance Thomas Gleixner
2025-03-02 19:37 ` [patch V2 12/17] posix-timers: Switch to jhash32() Thomas Gleixner
2025-03-02 19:37 ` [patch V2 13/17] posix-timers: Avoid false cacheline sharing Thomas Gleixner
2025-03-02 19:37 ` [patch V2 14/17] posix-timers: Make per process list RCU safe Thomas Gleixner
2025-03-02 19:37 ` [patch V2 15/17] posix-timers: Dont iterate /proc/$PID/timers with sighand::siglock held Thomas Gleixner
2025-03-02 19:37 ` [patch V2 16/17] posix-timers: Provide a mechanism to allocate a given timer ID Thomas Gleixner
2025-03-02 19:37 ` [patch V2 17/17] selftests/timers/posix-timers: Add a test for exact allocation mode Thomas Gleixner
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