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From: David Laight <David.Laight@ACULAB.COM>
To: 'James Simmons' <jsimmons@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"devel@driverdev.osuosl.org" <devel@driverdev.osuosl.org>,
	Andreas Dilger <andreas.dilger@intel.com>,
	"Oleg Drokin" <oleg.drokin@intel.com>,
	Lai Siyao <lai.siyao@intel.com>,
	"Jinshan Xiong" <jinshan.xiong@intel.com>,
	NeilBrown <neilb@suse.com>
Cc: Gu Zheng <gzheng@ddn.com>, Li Xi <lixi@ddn.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Lustre Development List <lustre-devel@lists.lustre.org>
Subject: RE: [PATCH 1/4] staging: lustre: obdclass: change spinlock of key to rwlock
Date: Thu, 3 May 2018 13:50:07 +0000	[thread overview]
Message-ID: <a3594bd7c393418c8fda5150a075ff1a@AcuMS.aculab.com> (raw)
In-Reply-To: <1525285308-15347-2-git-send-email-jsimmons@infradead.org>

From: James Simmons
> Sent: 02 May 2018 19:22
> From: Li Xi <lixi@ddn.com>
> 
> Most of the time, keys are never changed. So rwlock might be
> better for the concurrency of key read.

OTOH unless there is contention on the spin lock during reads the
additional cost of a rwlock (probably double that of a spinlock)
will hurt performance.

...
> -	spin_lock(&lu_keys_guard);
> +	read_lock(&lu_keys_guard);
>  	atomic_inc(&lu_key_initing_cnt);
> -	spin_unlock(&lu_keys_guard);
> +	read_unlock(&lu_keys_guard);

WTF, seems unlikely that you need to hold any kind of lock
over an atomic_inc().

If this is just ensuring that no code holds the lock then
it would need to request the write_lock().
(and would need a comment)

	David

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WARNING: multiple messages have this Message-ID (diff)
From: David Laight <David.Laight@ACULAB.COM>
To: 'James Simmons' <jsimmons@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"devel@driverdev.osuosl.org" <devel@driverdev.osuosl.org>,
	Andreas Dilger <andreas.dilger@intel.com>,
	Oleg Drokin <oleg.drokin@intel.com>,
	Lai Siyao <lai.siyao@intel.com>,
	Jinshan Xiong <jinshan.xiong@intel.com>,
	NeilBrown <neilb@suse.com>
Cc: Gu Zheng <gzheng@ddn.com>, Li Xi <lixi@ddn.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Lustre Development List <lustre-devel@lists.lustre.org>
Subject: [lustre-devel] [PATCH 1/4] staging: lustre: obdclass: change spinlock of key to rwlock
Date: Thu, 3 May 2018 13:50:07 +0000	[thread overview]
Message-ID: <a3594bd7c393418c8fda5150a075ff1a@AcuMS.aculab.com> (raw)
In-Reply-To: <1525285308-15347-2-git-send-email-jsimmons@infradead.org>

From: James Simmons
> Sent: 02 May 2018 19:22
> From: Li Xi <lixi@ddn.com>
> 
> Most of the time, keys are never changed. So rwlock might be
> better for the concurrency of key read.

OTOH unless there is contention on the spin lock during reads the
additional cost of a rwlock (probably double that of a spinlock)
will hurt performance.

...
> -	spin_lock(&lu_keys_guard);
> +	read_lock(&lu_keys_guard);
>  	atomic_inc(&lu_key_initing_cnt);
> -	spin_unlock(&lu_keys_guard);
> +	read_unlock(&lu_keys_guard);

WTF, seems unlikely that you need to hold any kind of lock
over an atomic_inc().

If this is just ensuring that no code holds the lock then
it would need to request the write_lock().
(and would need a comment)

	David

  reply	other threads:[~2018-05-03 13:50 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-02 18:21 [PATCH 0/4] staging: lustre: obdclass: missing lu_object fixes James Simmons
2018-05-02 18:21 ` [lustre-devel] " James Simmons
2018-05-02 18:21 ` [PATCH 1/4] staging: lustre: obdclass: change spinlock of key to rwlock James Simmons
2018-05-02 18:21   ` [lustre-devel] " James Simmons
2018-05-03 13:50   ` David Laight [this message]
2018-05-03 13:50     ` David Laight
2018-05-03 23:26     ` NeilBrown
2018-05-03 23:26       ` [lustre-devel] " NeilBrown
2018-05-04  0:11     ` Dilger, Andreas
2018-05-04  0:11       ` [lustre-devel] " Dilger, Andreas
2018-05-04  0:53       ` NeilBrown
2018-05-04  0:53         ` [lustre-devel] " NeilBrown
2018-05-02 18:21 ` [PATCH 2/4] staging: lustre: obdclass: hoist locking in lu_context_exit() James Simmons
2018-05-02 18:21   ` [lustre-devel] " James Simmons
2018-05-02 18:21 ` [PATCH 3/4] staging: lustre: obdclass: guarantee all keys filled James Simmons
2018-05-02 18:21   ` [lustre-devel] " James Simmons
2018-05-02 18:21 ` [PATCH 4/4] staging: lustre: obdclass: change object lookup to no wait mode James Simmons
2018-05-02 18:21   ` [lustre-devel] " James Simmons
2018-05-04  1:15   ` NeilBrown
2018-05-04  1:15     ` [lustre-devel] " NeilBrown
2018-05-15  0:37     ` James Simmons
2018-05-15  0:37       ` [lustre-devel] " James Simmons
2018-05-15  1:37       ` NeilBrown
2018-05-15  1:37         ` [lustre-devel] " NeilBrown
2018-05-15  2:11         ` James Simmons
2018-05-15  2:11           ` [lustre-devel] " James Simmons
2018-05-07  1:47   ` Greg Kroah-Hartman
2018-05-07  1:47     ` [lustre-devel] " Greg Kroah-Hartman
2018-05-08 11:45   ` Dan Carpenter
2018-05-08 11:45     ` [lustre-devel] " Dan Carpenter
2018-05-15 15:02     ` James Simmons
2018-05-15 15:02       ` [lustre-devel] " James Simmons
2018-05-16  8:00       ` Dan Carpenter
2018-05-16  8:00         ` [lustre-devel] " Dan Carpenter
2018-05-16  9:12         ` Dilger, Andreas
2018-05-16  9:12           ` [lustre-devel] " Dilger, Andreas
2018-05-16 15:44           ` Joe Perches
2018-05-16 15:44             ` [lustre-devel] " Joe Perches
2018-05-16 16:57       ` Greg Kroah-Hartman
2018-05-16 16:57         ` [lustre-devel] " Greg Kroah-Hartman
2018-05-17  5:07         ` James Simmons
2018-05-17  5:07           ` [lustre-devel] " James Simmons

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