| Message ID | 1463566690-22881-1-git-send-email-shamir.rabinovitch@oracle.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
On Wed, May 18, 2016 at 06:18:10AM -0400, Shamir Rabinovitch wrote: > From: shamir rabinovitch <shamir.rabinovitch@oracle.com> > > The problem is that the function 'send_reply_to_slave' get the > 'req_sa_mad' as pointer whose address can be unaligned to 8 bytes. > In this case the compiler cannot know in advance what will be the > alignment of the 'data' field. > > Sowmini Varadhan pointed to this reply from Dave Miller that say > that memcpy should not be used to solve alignment issues: > https://lkml.org/lkml/2015/10/21/352 > > Optimization of memcpy to 'ldx' instruction can only happen if the > compiler see that the size of the data we copy is 8 bytes and it > assume it is aligned to 8. If the compiler know the type is not > aligned to 8 it must not optimize the 8 bytes copy. Defining the > data type as aligned to 4 force the compiler to assume it is not > aligned to 8 at all time. > > Full credit for the idea goes to Jason Gunthorpe > <jgunthorpe@obsidianresearch.com>. You can use Suggested-By tag for that purpose. > > v3: Change patch according to suggestion by Jason Gunthorpe > <jgunthorpe@obsidianresearch.com> > > v2: Minor fix in patch headline by Or Gerlitz <gerlitz.or@gmail.com> > > Signed-off-by: shamir rabinovitch <shamir.rabinovitch@oracle.com> s/shamir/Shamir s/rabinovitch/Rabinovitch > --- > drivers/infiniband/hw/mlx4/mcg.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/drivers/infiniband/hw/mlx4/mcg.c b/drivers/infiniband/hw/mlx4/mcg.c > index 99451d8..0550017 100644 > --- a/drivers/infiniband/hw/mlx4/mcg.c > +++ b/drivers/infiniband/hw/mlx4/mcg.c > @@ -96,7 +96,7 @@ struct ib_sa_mcmember_data { > u8 scope_join_state; > u8 proxy_join; > u8 reserved[2]; > -}; > +} __packed __aligned(4); > > struct mcast_group { > struct ib_sa_mcmember_data rec; > -- > 1.7.1 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-rdma" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 05/18/2016 06:18 AM, shamir.rabinovitch@oracle.com wrote: > From: shamir rabinovitch <shamir.rabinovitch@oracle.com> > > The problem is that the function 'send_reply_to_slave' get the > 'req_sa_mad' as pointer whose address can be unaligned to 8 bytes. > In this case the compiler cannot know in advance what will be the > alignment of the 'data' field. > > Sowmini Varadhan pointed to this reply from Dave Miller that say > that memcpy should not be used to solve alignment issues: > https://lkml.org/lkml/2015/10/21/352 > > Optimization of memcpy to 'ldx' instruction can only happen if the > compiler see that the size of the data we copy is 8 bytes and it > assume it is aligned to 8. If the compiler know the type is not > aligned to 8 it must not optimize the 8 bytes copy. Defining the > data type as aligned to 4 force the compiler to assume it is not > aligned to 8 at all time. > > Full credit for the idea goes to Jason Gunthorpe > <jgunthorpe@obsidianresearch.com>. > > v3: Change patch according to suggestion by Jason Gunthorpe > <jgunthorpe@obsidianresearch.com> > > v2: Minor fix in patch headline by Or Gerlitz <gerlitz.or@gmail.com> > > Signed-off-by: shamir rabinovitch <shamir.rabinovitch@oracle.com> I considerably reworked the commit message, but otherwise applied. Thanks.
diff --git a/drivers/infiniband/hw/mlx4/mcg.c b/drivers/infiniband/hw/mlx4/mcg.c index 99451d8..0550017 100644 --- a/drivers/infiniband/hw/mlx4/mcg.c +++ b/drivers/infiniband/hw/mlx4/mcg.c @@ -96,7 +96,7 @@ struct ib_sa_mcmember_data { u8 scope_join_state; u8 proxy_join; u8 reserved[2]; -}; +} __packed __aligned(4); struct mcast_group { struct ib_sa_mcmember_data rec;