| Message ID | 20200930051722.389587-1-anant.thazhemadam@gmail.com |
|---|---|
| Headers | show |
| Series | reorder members of structures in virtio_net for optimization | expand |
From: Anant Thazhemadam <anant.thazhemadam@gmail.com> Date: Wed, 30 Sep 2020 10:47:20 +0530 > The structures virtnet_info and receive_queue have byte holes in > middle, and their members could do with some rearranging > (order-of-declaration wise) in order to overcome this. > > Rearranging the members helps in: > * elimination the byte holes in the middle of the structures > * reduce the size of the structure (virtnet_info) > * have more members stored in one cache line (as opposed to > unnecessarily crossing the cacheline boundary and spanning > different cachelines) > > The analysis was performed using pahole. > > These patches may be applied in any order. What effects do these changes have on performance? The cache locality for various TX and RX paths could be effected. I'm not applying these patches without some data on the performance impact. Thank you.
On Fri, Oct 02, 2020 at 07:06:38PM -0700, David Miller wrote: > From: Anant Thazhemadam <anant.thazhemadam@gmail.com> > Date: Wed, 30 Sep 2020 10:47:20 +0530 > > > The structures virtnet_info and receive_queue have byte holes in > > middle, and their members could do with some rearranging > > (order-of-declaration wise) in order to overcome this. > > > > Rearranging the members helps in: > > * elimination the byte holes in the middle of the structures > > * reduce the size of the structure (virtnet_info) > > * have more members stored in one cache line (as opposed to > > unnecessarily crossing the cacheline boundary and spanning > > different cachelines) > > > > The analysis was performed using pahole. > > > > These patches may be applied in any order. > > What effects do these changes have on performance? > > The cache locality for various TX and RX paths could be effected. > > I'm not applying these patches without some data on the performance > impact. > > Thank you. Agree wholeheartedly.
The structures virtnet_info and receive_queue have byte holes in middle, and their members could do with some rearranging (order-of-declaration wise) in order to overcome this. Rearranging the members helps in: * elimination the byte holes in the middle of the structures * reduce the size of the structure (virtnet_info) * have more members stored in one cache line (as opposed to unnecessarily crossing the cacheline boundary and spanning different cachelines) The analysis was performed using pahole. These patches may be applied in any order. Anant Thazhemadam (2): net: reorder members of virtnet_info for optimization net: reorder members of receive_queue in virtio_net for optimization drivers/net/virtio_net.c | 44 +++++++++++++++++++++------------------- 1 file changed, 23 insertions(+), 21 deletions(-)