linux-kernel - Re: [PATCH 1/5] locking: Introduce range reader/writer lock

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Message-ID: <20170329085626.rtudonk7bqzoy3vm@hirez.programming.kicks-ass.net>
Date:   Wed, 29 Mar 2017 10:56:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     mingo@...nel.org, akpm@...ux-foundation.org, jack@...e.cz,
        kirill.shutemov@...ux.intel.com, mhocko@...e.com,
        mgorman@...hsingularity.net, linux-kernel@...r.kernel.org,
        Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 1/5] locking: Introduce range reader/writer lock

On Mon, Mar 06, 2017 at 09:03:26PM -0800, Davidlohr Bueso wrote:
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 88e01e08e279..e4d9eadd2c47 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -154,7 +154,6 @@ config DRM_RADEON
>  	select HWMON
>  	select BACKLIGHT_CLASS_DEVICE
>  	select BACKLIGHT_LCD_SUPPORT
> -	select INTERVAL_TREE
>  	help
>  	  Choose this option if you have an ATI Radeon graphics card.  There
>  	  are both PCI and AGP versions.  You don't need to choose this to
> @@ -174,7 +173,6 @@ config DRM_AMDGPU
>  	select HWMON
>  	select BACKLIGHT_CLASS_DEVICE
>  	select BACKLIGHT_LCD_SUPPORT
> -	select INTERVAL_TREE
>  	help
>  	  Choose this option if you have a recent AMD Radeon graphics card.
>  
> diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
> index 183f5dc1c3f2..8a9154550f46 100644
> --- a/drivers/gpu/drm/i915/Kconfig
> +++ b/drivers/gpu/drm/i915/Kconfig
> @@ -3,7 +3,6 @@ config DRM_I915
>  	depends on DRM
>  	depends on X86 && PCI
>  	select INTEL_GTT
> -	select INTERVAL_TREE
>  	# we need shmfs for the swappable backing store, and in particular
>  	# the shmem_readpage() which depends upon tmpfs
>  	select SHMEM

I presume this is part of making INTERVAL_TREE unconditional; should be
a separate patch, no?


> +/*
> + * The largest range will span [0,RANGE_RWLOCK_INFINITY].
> + */
> +#define RANGE_RWLOCK_INFINITY  (~0UL - 1)

That's a strange limit, what's wrong with ~0UL ?

> +
> +struct range_rwlock {
> +	struct interval_tree_node node;
> +	struct task_struct *task;
> +	/* Number of ranges which are blocking acquisition of the lock */
> +	unsigned int blocking_ranges;
> +	bool reader;
> +};

Hate the name; our rwlock is a spinlock, therefore this thing suggests
it is too.

Also, no bool in structures.