Subject: Re: [PATCH V2 3/6] powerpc/powernv: use one M64 BAR in Single PE mode for one VF BAR

From: Gavin Shan <[email-masked]>
Date: Thu, 6 Aug 2015 20:07:01 +1000

On Thu, Aug 06, 2015 at 05:36:02PM +0800, Wei Yang wrote:
>On Thu, Aug 06, 2015 at 03:20:25PM +1000, Gavin Shan wrote:
>>On Wed, Aug 05, 2015 at 09:25:00AM +0800, Wei Yang wrote:
>>>In current implementation, when VF BAR is bigger than 64MB, it uses 4 M64
>>>BAR in Single PE mode to cover the number of VFs required to be enabled.
>>>By doing so, several VFs would be in one VF Group and leads to interference
>>>between VFs in the same group.
>>>
>>>This patch changes the design by using one M64 BAR in Single PE mode for
>>>one VF BAR. This gives absolute isolation for VFs.
>>>
>>>Signed-off-by: Wei Yang <[email-masked]>
>>>---
>>> arch/powerpc/include/asm/pci-bridge.h     |    5 +-
>>> arch/powerpc/platforms/powernv/pci-ioda.c |  180 ++++++++++++-----------------
>>> 2 files changed, 76 insertions(+), 109 deletions(-)
>>>
>>>diff --git a/arch/powerpc/include/asm/pci-bridge.h b/arch/powerpc/include/asm/pci-bridge.h
>>>index 712add5..8aeba4c 100644
>>>--- a/arch/powerpc/include/asm/pci-bridge.h
>>>+++ b/arch/powerpc/include/asm/pci-bridge.h
>>>@@ -214,10 +214,9 @@ struct pci_dn {
>>> 	u16     vfs_expanded;		/* number of VFs IOV BAR expanded */
>>> 	u16     num_vfs;		/* number of VFs enabled*/
>>> 	int     offset;			/* PE# for the first VF PE */
>>>-#define M64_PER_IOV 4
>>>-	int     m64_per_iov;
>>>+	bool    m64_single_mode;	/* Use M64 BAR in Single Mode */
>>> #define IODA_INVALID_M64        (-1)
>>>-	int     m64_wins[PCI_SRIOV_NUM_BARS][M64_PER_IOV];
>>>+	int     (*m64_map)[PCI_SRIOV_NUM_BARS];
>>
>>It can be explicit? For example:
>>
>>	int	*m64_map;
>>
>>	/* Initialization */
>>	size_t size = sizeof(*pdn->m64_map) * PCI_SRIOV_NUM_BARS * num_of_max_VFs;
>>	pdn->m64_map = kmalloc(size, GFP_KERNEL);
>>	for (i = 0; i < PCI_SRIOV_NUM_BARS; i++)
>>		for (j = 0; j < num_of_max_VFs; j++)
>>			pdn->m64_map[i * PCI_SRIOV_NUM_BARS + j] = PNV_INVALID_M64;
>>
>>	/* Destroy */
>>	int step = 1;
>>
>>	if (!pdn->m64_single_mode)
>>		step = phb->ioda.total_pe;
>>	for (i = 0; i < PCI_SRIOV_NUM_BARS * num_of_max_VFs; i += step)
>>		if (pdn->m64_map[i] == PNV_INVALID_M64)
>>			continue;
>>
>>		/* Unmap the window */
>>	
>
>The m64_map is a pointer to an array with 6 elements, which represents the 6
>M64 BAR index for the 6 VF BARs.
>
>    When we use Shared Mode, one array is allocated. The six elements
>    represents the six M64 BAR(at most) used to map the whole IOV BAR.
>
>    When we use Single Mode, num_vfs array is allocate. Each array represents
>    the map between one VF's BAR and M64 BAR index.
>
>During the map and un-map, M64 BAR is assigned one by one in VF BAR's order.
>So I think the code is explicit.
>
>In your code, you allocate a big one dimension array to hold the M64 BAR
>index. It works, while I don't think this is more explicit than original code.
>

When M64 is in Single Mode, array with (num_vfs * 6) entries is allocated
because every VF BAR (6 at most) will have one corresponding PHB M64 BAR.
Anything I missed?

The point in my code is you needn't worry about the mode (single vs shared)
As I said, not too much memory wasted. However, it's up to you.

I'm not fan of "int (*m64_map)[PCI_SRIOV_NUM_BARS]". Instead, you can replace
it with "int *m64_map" and calculate its size using following formula:

	sizeof(*pdn->m64_map) * PCI_SRIOV_NUM_BARS;

	sizeof(*pdn->m64_map) * PCI_SRIOV_NUM_BARS * num_vfs;

>-- 
>Richard Yang
>Help you, Help me