This is a performance optimization for the fdtable code. When expanding the
fdtable for a task, we want to allocate at least L1_CACHE_BYTES for the new
fdset memory -- this will ensure that the fdsets of two different tasks will
not share the same cacheline, causing lots of cacheline ping-pongs.
Signed-off-by: Vadim Lobanov <[email protected]>
diff -Npru old/fs/file.c new/fs/file.c
--- old/fs/file.c 2006-10-14 15:40:12.000000000 -0700
+++ new/fs/file.c 2006-10-14 15:50:00.000000000 -0700
@@ -178,7 +178,8 @@ static struct fdtable * alloc_fdtable(un
if (!data)
goto out_fdt;
fdt->fd = (struct file **)data;
- data = alloc_fdmem(2 * nr / BITS_PER_BYTE);
+ data = alloc_fdmem(max_t(unsigned int,
+ 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
if (!data)
goto out_arr;
fdt->open_fds = (fd_set *)data;