Re: [PATCH v4 06/12] xen/spinlock: make struct lock_profile rspinlock_t aware

From: Julien Grall <julien@xen.org>
To: Juergen Gross <jgross@suse.com>, xen-devel@lists.xenproject.org
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	Jan Beulich <jbeulich@suse.com>,
	Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
	Alejandro Vallejo <alejandro.vallejo@cloud.com>
Subject: Re: [PATCH v4 06/12] xen/spinlock: make struct lock_profile rspinlock_t aware
Date: Tue, 12 Dec 2023 18:42:55 +0000	[thread overview]
Message-ID: <ba842318-0d5e-4b8f-99f9-f0f1e2dda1ab@xen.org> (raw)
In-Reply-To: <20231212094725.22184-7-jgross@suse.com>

Hi,

On 12/12/2023 09:47, Juergen Gross wrote:
> Struct lock_profile contains a pointer to the spinlock it is associated
> with. Prepare support of differing spinlock_t and rspinlock_t types by
> adding a type indicator of the pointer. Use the highest bit of the
> block_cnt member for this indicator in order to not grow the struct
> while hurting only the slow path with slightly less performant code.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>
> Acked-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
> ---
> V2:
> - new patch
> ---
>   xen/common/spinlock.c      | 26 +++++++++++++++++++-------
>   xen/include/xen/spinlock.h | 10 ++++++++--
>   2 files changed, 27 insertions(+), 9 deletions(-)
> 
> diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c
> index c1a9ba1304..7d611d3d7d 100644
> --- a/xen/common/spinlock.c
> +++ b/xen/common/spinlock.c
> @@ -538,19 +538,31 @@ static void spinlock_profile_iterate(lock_profile_subfunc *sub, void *par)
>   static void cf_check spinlock_profile_print_elem(struct lock_profile *data,
>       int32_t type, int32_t idx, void *par)
>   {
> -    struct spinlock *lock = data->lock;
> +    unsigned int cpu;
> +    uint32_t lockval;
> +
> +    if ( data->is_rlock )
> +    {
> +        cpu = data->rlock->debug.cpu;
> +        lockval = data->rlock->tickets.head_tail;
> +    }
> +    else
> +    {
> +        cpu = data->lock->debug.cpu;
> +        lockval = data->lock->tickets.head_tail;
> +    }
>   
>       printk("%s ", lock_profile_ancs[type].name);
>       if ( type != LOCKPROF_TYPE_GLOBAL )
>           printk("%d ", idx);
> -    printk("%s: addr=%p, lockval=%08x, ", data->name, lock,
> -           lock->tickets.head_tail);
> -    if ( lock->debug.cpu == SPINLOCK_NO_CPU )
> +    printk("%s: addr=%p, lockval=%08x, ", data->name, data->lock, lockval);
> +    if ( cpu == SPINLOCK_NO_CPU )
>           printk("not locked\n");
>       else
> -        printk("cpu=%d\n", lock->debug.cpu);
> -    printk("  lock:%" PRId64 "(%" PRI_stime "), block:%" PRId64 "(%" PRI_stime ")\n",
> -           data->lock_cnt, data->time_hold, data->block_cnt, data->time_block);
> +        printk("cpu=%u\n", cpu);
> +    printk("  lock:%" PRIu64 "(%" PRI_stime "), block:%" PRIu64 "(%" PRI_stime ")\n",
> +           data->lock_cnt, data->time_hold, (uint64_t)data->block_cnt,
> +           data->time_block);
>   }
>   
>   void cf_check spinlock_profile_printall(unsigned char key)
> diff --git a/xen/include/xen/spinlock.h b/xen/include/xen/spinlock.h
> index 05b97c1e03..ac3bef267a 100644
> --- a/xen/include/xen/spinlock.h
> +++ b/xen/include/xen/spinlock.h
> @@ -76,13 +76,19 @@ union lock_debug { };
>   */
>   
>   struct spinlock;
> +/* Temporary hack until a dedicated struct rspinlock is existing. */
> +#define rspinlock spinlock
>   
>   struct lock_profile {
>       struct lock_profile *next;       /* forward link */
>       const char          *name;       /* lock name */
> -    struct spinlock     *lock;       /* the lock itself */
> +    union {
> +        struct spinlock *lock;       /* the lock itself */
> +        struct rspinlock *rlock;     /* the recursive lock itself */
> +    };
>       uint64_t            lock_cnt;    /* # of complete locking ops */
> -    uint64_t            block_cnt;   /* # of complete wait for lock */
> +    uint64_t            block_cnt:63; /* # of complete wait for lock */
> +    uint64_t            is_rlock:1;  /* use rlock pointer */

This is meant to act like a bool. So I would prefer if we use:

bool is_rwlock:1;

And then use true/false when set.

Acked-by: Julien Grall <jgrall@amazon.com>

>       s_time_t            time_hold;   /* cumulated lock time */
>       s_time_t            time_block;  /* cumulated wait time */
>       s_time_t            time_locked; /* system time of last locking */

Cheers,

-- 
Julien Grall