Re: [PATCH v1 3/3] kernel/resource: cleanup and optimize iomem_is_exclusive()

[David Hildenbrand]

On 12.08.21 09:14, Andy Shevchenko wrote:
> On Thursday, August 12, 2021, David Hildenbrand <david@xxxxxxxxxx 
> <mailto:david@xxxxxxxxxx>> wrote:
>
>     On 11.08.21 22:47, Andy Shevchenko wrote:
>
>
>
>         On Wednesday, August 11, 2021, David Hildenbrand
>         <david@xxxxxxxxxx <mailto:david@xxxxxxxxxx>
>         <mailto:david@xxxxxxxxxx <mailto:david@xxxxxxxxxx>>> wrote:
>
>              Let's clean it up a bit, removing the unnecessary usage of
>         r_next() by
>              next_resource(), and use next_range_resource() in case we
>         are not
>              interested in a certain subtree.
>
>              Signed-off-by: David Hildenbrand <david@xxxxxxxxxx
>         <mailto:david@xxxxxxxxxx>
>              <mailto:david@xxxxxxxxxx <mailto:david@xxxxxxxxxx>>>
>              ---
>                kernel/resource.c | 19 +++++++++++--------
>                1 file changed, 11 insertions(+), 8 deletions(-)
>
>              diff --git a/kernel/resource.c b/kernel/resource.c
>              index 2938cf520ca3..ea853a075a83 100644
>              --- a/kernel/resource.c
>              +++ b/kernel/resource.c
>              @@ -1754,9 +1754,8 @@ static int strict_iomem_checks;
>                 */
>                bool iomem_is_exclusive(u64 addr)
>                {
>              -       struct resource *p = &iomem_resource;
>              +       struct resource *p;
>                       bool err = false;
>              -       loff_t l;
>                       int size = PAGE_SIZE;
>
>                       if (!strict_iomem_checks)
>              @@ -1765,27 +1764,31 @@ bool iomem_is_exclusive(u64 addr)
>                       addr = addr & PAGE_MASK;
>
>                       read_lock(&resource_lock);
>              -       for (p = p->child; p ; p = r_next(NULL, p, &l)) {
>              +       for (p = iomem_resource.child; p ;) {
>
>
>     Hi Andy,
>
>
>         I consider the ordinal part of p initialization is slightly
>         better and done outside of read lock.
>
>         Something like
>         p= &iomem_res...;
>         read lock
>         for (p = p->child; ...) {
>
>
>     Why should we care about doing that outside of the lock? That smells
>     like a micro-optimization the compiler will most probably overwrite
>     either way as the address of iomem_resource is just constant?
>
>     Also, for me it's much more readable and compact if we perform a
>     single initialization instead of two separate ones in this case.
>
>     We're using the pattern I use in, find_next_iomem_res() and
>     __region_intersects(), while we use the old pattern in
>     iomem_map_sanity_check(), where we also use the same unnecessary
>     r_next() call.
>
>     I might just cleanup iomem_map_sanity_check() in a similar way.
>
>
>
> Yes, it’s like micro optimization. If you want your way I suggest then 
> to add a macro
>
> #define for_each_iomem_resource_child() \
>   for (iomem_resource...)

I think the only thing that really makes sense would be something like this on top (not compiled yet):


diff --git a/kernel/resource.c b/kernel/resource.c
index ea853a075a83..35aaa72df0ce 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -80,6 +80,11 @@ static struct resource *next_resource_skip_children(struct resource *p)
        return p->sibling;
 }
 
+#define for_each_resource(_root, _p, _skip_children) \
+       for ((_p) = (_root)->child; (_p); \
+            (_p) = (_skip_children) ? next_resource_skip_children(_p) : \
+                                      next_resource(_p))
+
 static void *r_next(struct seq_file *m, void *v, loff_t *pos)
 {
        struct resource *p = v;
@@ -1714,16 +1719,16 @@ int iomem_map_sanity_check(resource_size_t addr, unsigned long size)
 bool iomem_range_contains_excluded(u64 addr, u64 size)
 {
        const unsigned int flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_EXCLUSIVE;
-       bool excluded = false;
+       bool skip_children, excluded = false;
        struct resource *p;
 
        read_lock(&resource_lock);
-       for (p = iomem_resource.child; p ;) {
+       for_each_resource(&iomem_resource, p, skip_children) {
                if (p->start >= addr + size)
                        break;
                if (p->end < addr) {
                        /* No need to consider children */
-                       p = next_resource_skip_children(p);
+                       skip_children = true;
                        continue;
                }
                /*
@@ -1735,7 +1740,7 @@ bool iomem_range_contains_excluded(u64 addr, u64 size)
                        excluded = true;
                        break;
                }
-               p = next_resource(p);
+               skip_children = false;
        }
        read_unlock(&resource_lock);
 
@@ -1755,7 +1760,7 @@ static int strict_iomem_checks;
 bool iomem_is_exclusive(u64 addr)
 {
        struct resource *p;
-       bool err = false;
+       bool skip_children, err = false;
        int size = PAGE_SIZE;
 
        if (!strict_iomem_checks)
@@ -1764,7 +1769,7 @@ bool iomem_is_exclusive(u64 addr)
        addr = addr & PAGE_MASK;
 
        read_lock(&resource_lock);
-       for (p = iomem_resource.child; p ;) {
+       for_each_resource(&iomem_resource, p, skip_children) {
                /*
                 * We can probably skip the resources without
                 * IORESOURCE_IO attribute?
@@ -1773,7 +1778,7 @@ bool iomem_is_exclusive(u64 addr)
                        break;
                if (p->end < addr) {
                        /* No need to consider children */
-                       p = next_resource_skip_children(p);
+                       skip_children = true;
                        continue;
                }
 
@@ -1788,7 +1793,7 @@ bool iomem_is_exclusive(u64 addr)
                        err = true;
                        break;
                }
-               p = next_resource(p);
+               skip_children = false;
        }
        read_unlock(&resource_lock);
 


Thoughts?


--
Thanks,

David / dhildenb