Re: [RFC PATCH 2/3] x86/io: implement 256-bit IO read and write

On Tuesday, March 03/20/18, 2018 at 20:10:19 +0530, David Laight wrote:

From: Rahul Lakkireddy

quoted

Sent: 20 March 2018 13:32

...

quoted

On High Availability Server, the logs of the failing system must be
collected as quickly as possible.  So, we're concerned with the amount
of time taken to collect our large on-chip memory.  We see improvement
in doing 256-bit reads at a time.

Two other options:

1) Get the device to DMA into host memory.

Unfortunately, our device doesn't support doing DMA of on-chip memory.

2) Use mmap() (and vm_iomap_memory() in your driver) to get direct
   userspace access to the (I assume) PCIe memory space.
   You can then use whatever copy instructions the cpu has.
   (Just don't use memcpy().)

We also need to collect this in kernel space i.e. from crash recovery
kernel.

Thanks,
Rahul