Manfred Spraul writes:
> I've run my slab microbenchmark over the 3 versions:
> - current
> - generic_fls
> - i386 asm optimized fls
>
> The test reports the fastest time for 100 kmalloc calls in a tight loop
> (Duron 700). Loop/test overhead substracted.
>
> 32-byte alloc:
> current: 41 ticks
> generic_fls: 56 ticks
> bsrl: 54 ticks
>
> 4096 byte alloc: 84 ticks
> generic_fls: 53 ticks
> bsrl: 54 ticks
>
> 40 ticks difference for -current between 4096 and 32 bytes - ~4 cycles
> for each loop.
> bit scan is 10 ticks slower for 32 byte allocs, 30 ticks faster for 4096
> byte allocs.
>
> No difference between generic_fls and bsrl - the branch predictor can
> easily predict all branches in generic_fls for constant kmalloc calls.
>
Most kmalloc calls get constant size argument (usually
sizeof(something)). So, if switch() is used in stead of loop (and
kmalloc made inline), compiler would be able to optimize away
cache_sizes[] selection completely. Attached (ugly) patch does this.
> --
Nikita.
===== include/linux/slab.h 1.13 vs edited =====
--- 1.13/include/linux/slab.h Thu Sep 26 04:41:05 2002
+++ edited/include/linux/slab.h Mon Oct 28 15:55:35 2002
@@ -58,8 +58,91 @@
extern void kmem_cache_free(kmem_cache_t *, void *);
extern unsigned int kmem_cache_size(kmem_cache_t *);
-extern void *kmalloc(size_t, int);
extern void kfree(const void *);
+extern void * __kmalloc (int i, size_t size, int flags);
+
+/**
+ * kmalloc - allocate memory
+ * @size: how many bytes of memory are required.
+ * @flags: the type of memory to allocate.
+ *
+ * kmalloc is the normal method of allocating memory
+ * in the kernel.
+ *
+ * The @flags argument may be one of:
+ *
+ * %GFP_USER - Allocate memory on behalf of user. May sleep.
+ *
+ * %GFP_KERNEL - Allocate normal kernel ram. May sleep.
+ *
+ * %GFP_ATOMIC - Allocation will not sleep. Use inside interrupt handlers.
+ *
+ * Additionally, the %GFP_DMA flag may be set to indicate the memory
+ * must be suitable for DMA. This can mean different things on different
+ * platforms. For example, on i386, it means that the memory must come
+ * from the first 16MB.
+ */
+static inline void * kmalloc (size_t size, int flags)
+{
+ int i;
+
+ switch(size) {
+#if PAGE_SIZE == 4096
+ case 0 ... 32:
+ i = 0;
+ break;
+ case 33 ... 64:
+#else
+ case 0 ... 64:
+#endif
+ i = 1;
+ break;
+ case 65 ... 96:
+ i = 2;
+ break;
+ case 97 ... 128:
+ i = 3;
+ break;
+ case 129 ... 192:
+ i = 4;
+ break;
+ case 193 ... 256:
+ i = 5;
+ break;
+ case 257 ... 512:
+ i = 6;
+ break;
+ case 513 ... 1024:
+ i = 7;
+ break;
+ case 1025 ... 2048:
+ i = 8;
+ break;
+ case 2049 ... 4096:
+ i = 9;
+ break;
+ case 4097 ... 8192:
+ i = 10;
+ break;
+ case 8193 ... 16384:
+ i = 11;
+ break;
+ case 16385 ... 32768:
+ i = 12;
+ break;
+ case 32769 ... 65536:
+ i = 13;
+ break;
+ case 65537 ... 131072:
+ i = 14;
+ break;
+ default:
+ return NULL;
+ }
+
+ return __kmalloc(i, size, flags);
+}
+
extern int FASTCALL(kmem_cache_reap(int));
===== mm/slab.c 1.33 vs edited =====
--- 1.33/mm/slab.c Sat Sep 28 18:23:50 2002
+++ edited/mm/slab.c Mon Oct 28 16:01:24 2002
@@ -1573,40 +1573,6 @@
}
/**
- * kmalloc - allocate memory
- * @size: how many bytes of memory are required.
- * @flags: the type of memory to allocate.
- *
- * kmalloc is the normal method of allocating memory
- * in the kernel.
- *
- * The @flags argument may be one of:
- *
- * %GFP_USER - Allocate memory on behalf of user. May sleep.
- *
- * %GFP_KERNEL - Allocate normal kernel ram. May sleep.
- *
- * %GFP_ATOMIC - Allocation will not sleep. Use inside interrupt handlers.
- *
- * Additionally, the %GFP_DMA flag may be set to indicate the memory
- * must be suitable for DMA. This can mean different things on different
- * platforms. For example, on i386, it means that the memory must come
- * from the first 16MB.
- */
-void * kmalloc (size_t size, int flags)
-{
- cache_sizes_t *csizep = cache_sizes;
-
- for (; csizep->cs_size; csizep++) {
- if (size > csizep->cs_size)
- continue;
- return __kmem_cache_alloc(flags & GFP_DMA ?
- csizep->cs_dmacachep : csizep->cs_cachep, flags);
- }
- return NULL;
-}
-
-/**
* kmem_cache_free - Deallocate an object
* @cachep: The cache the allocation was from.
* @objp: The previously allocated object.
@@ -1626,6 +1592,19 @@
local_irq_save(flags);
__kmem_cache_free(cachep, objp);
local_irq_restore(flags);
+}
+
+void * __kmalloc (int i, size_t size, int flags)
+{
+ cache_sizes_t *csizep;
+
+#if PAGE_SIZE == 4096
+ csizep = &cache_sizes[i];
+#else
+ csizep = &cache_sizes[i - 1];
+#endif
+ return kmem_cache_alloc(flags & GFP_DMA ?
+ csizep->cs_dmacachep : csizep->cs_cachep, flags);
}
/**
-
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This archive was generated by hypermail 2b29 : Thu Oct 31 2002 - 22:00:36 EST