I'd rather get rid of rwlocks altogether and use RCU in any cases where we
really have contention. Rwlocks don't help unless the read-side critical
sections are large enough to amortise the cache ping-pong cost of the
locking/unlocking operations. And in Xen we have very few if any
significantly sized critical sections.
I need to double check, but I believe we have only a couple of rwlock users
now, and none of the read-side critical sections are large, so in that case
I suggest we switch them to use spinlocks and kill our rwlock
implementation.
-- Keir
On 25/03/2011 16:49, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
> As a general library routine, it should behave as efficiently as
> possible, even if at present no significant contention is known here.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
>
> --- a/xen/common/rangeset.c
> +++ b/xen/common/rangeset.c
> @@ -25,7 +25,7 @@ struct rangeset {
>
> /* Ordered list of ranges contained in this set, and protecting lock. */
> struct list_head range_list;
> - spinlock_t lock;
> + rwlock_t lock;
>
> /* Pretty-printing name. */
> char name[32];
> @@ -103,7 +103,7 @@ int rangeset_add_range(
>
> ASSERT(s <= e);
>
> - spin_lock(&r->lock);
> + write_lock(&r->lock);
>
> x = find_range(r, s);
> y = find_range(r, e);
> @@ -159,7 +159,7 @@ int rangeset_add_range(
> }
>
> out:
> - spin_unlock(&r->lock);
> + write_unlock(&r->lock);
> return rc;
> }
>
> @@ -175,7 +175,7 @@ int rangeset_remove_range(
>
> ASSERT(s <= e);
>
> - spin_lock(&r->lock);
> + write_lock(&r->lock);
>
> x = find_range(r, s);
> y = find_range(r, e);
> @@ -231,7 +231,7 @@ int rangeset_remove_range(
> }
>
> out:
> - spin_unlock(&r->lock);
> + write_unlock(&r->lock);
> return rc;
> }
>
> @@ -243,10 +243,10 @@ int rangeset_contains_range(
>
> ASSERT(s <= e);
>
> - spin_lock(&r->lock);
> + read_lock(&r->lock);
> x = find_range(r, s);
> contains = (x && (x->e >= e));
> - spin_unlock(&r->lock);
> + read_unlock(&r->lock);
>
> return contains;
> }
> @@ -259,10 +259,10 @@ int rangeset_overlaps_range(
>
> ASSERT(s <= e);
>
> - spin_lock(&r->lock);
> + read_lock(&r->lock);
> x = find_range(r, e);
> overlaps = (x && (s <= x->e));
> - spin_unlock(&r->lock);
> + read_unlock(&r->lock);
>
> return overlaps;
> }
> @@ -274,13 +274,13 @@ int rangeset_report_ranges(
> struct range *x;
> int rc = 0;
>
> - spin_lock(&r->lock);
> + read_lock(&r->lock);
>
> for ( x = find_range(r, s); x && (x->s <= e) && !rc; x = next_range(r, x)
> )
> if ( x->e >= s )
> rc = cb(max(x->s, s), min(x->e, e), ctxt);
>
> - spin_unlock(&r->lock);
> + read_unlock(&r->lock);
>
> return rc;
> }
> @@ -318,7 +318,7 @@ struct rangeset *rangeset_new(
> if ( r == NULL )
> return NULL;
>
> - spin_lock_init(&r->lock);
> + rwlock_init(&r->lock);
> INIT_LIST_HEAD(&r->range_list);
>
> BUG_ON(flags & ~RANGESETF_prettyprint_hex);
> @@ -403,7 +403,7 @@ void rangeset_printk(
> int nr_printed = 0;
> struct range *x;
>
> - spin_lock(&r->lock);
> + read_lock(&r->lock);
>
> printk("%-10s {", r->name);
>
> @@ -422,7 +422,7 @@ void rangeset_printk(
>
> printk(" }");
>
> - spin_unlock(&r->lock);
> + read_unlock(&r->lock);
> }
>
> void rangeset_domain_printk(
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel
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