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

[David Hildenbrand <david@redhat.com>]

On 12.08.21 09:14, Andy Shevchenko wrote:
> 
> 
> On Thursday, August 12, 2021, David Hildenbrand <david@redhat.com 
> <mailto:david@redhat.com>> wrote:
> 
>     On 11.08.21 22:47, Andy Shevchenko wrote:
> 
> 
> 
>         On Wednesday, August 11, 2021, David Hildenbrand
>         <david@redhat.com <mailto:david@redhat.com>
>         <mailto:david@redhat.com <mailto:david@redhat.com>>> 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@redhat.com
>         <mailto:david@redhat.com>
>              <mailto:david@redhat.com <mailto:david@redhat.com>>>
>              ---
>                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