Re: [GIT PULL] iscsi-target merge for v3.1-rc1

Nicholas A. Bellinger
2011-07-26T07:00:42Z

On Mon, 2011-07-25 at 16:50 -0700, Andrew Morton wrote:
> On Mon, 25 Jul 2011 16:37:39 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
>
> > On Sat, 23 Jul 2011 16:16:15 -0700
> > "Nicholas A. Bellinger" <nab@linux-iscsi.org> wrote:
> >
> > > Please go ahead and pull from:
> > >
> > > master.kernel.org:/pub/scm/linux/kernel/git/nab/target-pending.git for-linus-merge
> >
> > i386 allyesconfig:
> >
> > ERROR: "__udivdi3" [drivers/target/target_core_mod.ko] undefined!
> >
> > somewhere in drivers/target/target_core_transport.c:transport_allocate_data_tasks().
>
> Probably the best place to fix this is within DIV_ROUND_UP(): make it
> handle 64-bits on 32-bit.
>
> This will have the pleasing side-effect of breaking
> drivers/scsi/cxgbi/cxgb4i/cxgb4i.c, which felt a need to duplicate the
> existing DIV_ROUND_UP() implementation.
>

Thanks for the input everyone. :)

How about the following to add a new DIV_ROUND_UP_ULL macro, and enable
it's usage within the offending transport_allocate_data_tasks() change
causing the regression in question for target_core_mod..?

Is there anything else that should be done to avoid unnecessary 64-bit
divide instruction slowness for generic 32-bit arch operation here..?

Thank you,

--nab

diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index a244c90..8032e1e 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -4054,17 +4054,16 @@ static int transport_allocate_data_tasks(
struct se_task *task;
struct se_device *dev = cmd->se_dev;
unsigned long flags;
- sector_t sectors;
int task_count, i, ret;
- sector_t dev_max_sectors = dev->se_sub_dev->se_dev_attrib.max_sectors;
+ sector_t sectors, dev_max_sectors = dev->se_sub_dev->se_dev_attrib.max_sectors;
u32 sector_size = dev->se_sub_dev->se_dev_attrib.block_size;
struct scatterlist *sg;
struct scatterlist *cmd_sg;

WARN_ON(cmd->data_length % sector_size);
sectors = DIV_ROUND_UP(cmd->data_length, sector_size);
- task_count = DIV_ROUND_UP(sectors, dev_max_sectors);
-
+ task_count = DIV_ROUND_UP_ULL(sectors, dev_max_sectors);
+
cmd_sg = sgl;
for (i = 0; i < task_count; i++) {
unsigned int task_size;
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 953352a..d66cba7 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -56,6 +56,17 @@

#define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f))
#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
+#define DIV_ROUND_UP_ULL(n,d) ( \
+{ \
+ unsigned long long _tmp = n, _off; \
+ int _res; \
+ /* Round up using asm/div64.h:do_div */ \
+ _off = do_div(_tmp, d); \
+ if (_off != 0) \
+ _tmp++; \
+ _res = _tmp; \
+} \
+)

/* The `const' in roundup() prevents gcc-3.3 from calling __divdi3 */
#define roundup(x, y) ( \