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From: Thomas Gleixner <tglx@linutronix.de>
To: "Matthew Wilcox \(Oracle\)" <willy@infradead.org>
Cc: neilb@suse.de, peterz@infradead.org, mingo@redhat.com,
	will@kernel.org, longman@redhat.com, boqun.feng@gmail.com,
	bigeasy@linutronix.de, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 02/17] locking: Add split_lock
Date: Mon, 12 Apr 2021 16:29:28 +0200	[thread overview]
Message-ID: <87blaj1sqf.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20210409025131.4114078-3-willy@infradead.org>

On Fri, Apr 09 2021 at 03:51, Matthew Wilcox wrote:
> Bitlocks do not currently participate in lockdep.  Conceptually, a
> bit_spinlock is a split lock, eg across each bucket in a hash table.
> The struct split_lock gives us somewhere to record the lockdep_map.

I like the concept, but the name is strange. The only purpose of 

> +struct split_lock {
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +	struct lockdep_map dep_map;
> +#endif
> +};

is to have a place to stick the lockdep map into. So it's not a lock
construct as the name suggests, it's just auxiliary data when lockdep is
enabled.

I know you hinted that RT could make use of that data structure and the
fact that it's mandatory for the various lock functions, but that's not
really feasible if this is related to a hash with a bit spinlock per
bucket as the data structure is hash global.

Sure, we can do pointer math to find out the bucket index and do
something from there, but I'm not sure whether that really helps. Need
to stare at the remaining few places where bit spinlocks are an issue on
RT.

Thanks,

        tglx



  reply	other threads:[~2021-04-12 14:29 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-09  2:51 [PATCH 00/17] Provide lockdep tracking for bit spin locks Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 01/17] x86: Rename split_lock_init to sld_init Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 02/17] locking: Add split_lock Matthew Wilcox (Oracle)
2021-04-12 14:29   ` Thomas Gleixner [this message]
2021-04-12 14:45     ` Matthew Wilcox
2021-04-12 15:01       ` Thomas Gleixner
2021-05-11  7:46       ` Peter Zijlstra
2021-04-09  2:51 ` [PATCH 03/17] bit_spinlock: Prepare for split_locks Matthew Wilcox (Oracle)
2021-04-09 14:32   ` Theodore Ts'o
2021-04-09 14:35     ` Matthew Wilcox
2021-04-09 14:55       ` Theodore Ts'o
2021-04-09  2:51 ` [PATCH 04/17] hlist_bl: " Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 05/17] dm-snap: Add dm_exceptional_lock Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 06/17] dcache: Add d_hash_lock Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 07/17] fscache: Add cookie_hash_lock Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 08/17] gfs2: Add qd_hash_lock Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 09/17] mbcache: Add mb_cache_lock Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 10/17] hlist_bl: Make the split_lock parameter mandatory Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 11/17] s390: Add airq_iv_lock Matthew Wilcox (Oracle)
2021-04-09  6:18   ` kernel test robot
2021-04-09 13:20     ` Matthew Wilcox
2021-04-09  2:51 ` [PATCH 12/17] zram: Add zram_table_lock Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 13/17] jbd2: Add jbd2_jh_lock Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 14/17] slub: Add slab_page_lock Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 15/17] zsmalloc: Add zs_pin_lock Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 16/17] rhashtable: Convert to split_lock Matthew Wilcox (Oracle)
2021-04-09  2:51 ` [PATCH 17/17] bit_spinlock: Track bit spin locks with lockdep Matthew Wilcox (Oracle)
2021-04-09  6:37   ` kernel test robot

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