[Xen-devel] RE: Rather slow time of Pin in Windows with GPL PV driver

[MaoXiaoyun <tinnycloud@xxxxxxxxxxx>]

Hi James:
 
      I did some more test, add some log to what the interrupts distribution.
      In XenNet_RxBufferCheck I log the CPU number by adding line
      KdPrint((__DRIVER_NAME "    pcpu = %lu\n", pcpu));  please refer to below code.
 
      Result below show that when KeSetTargetProcessorDpc is commentten, the interrupts
distribute over all VCPUs, could this explain something?
 
      Beside, I did some perf test using netperf, no performanc difference observed.
 
===============Result================================
      1) KeSetTargetProcessorDpc(&xi->rx_dpc, 0) is commentted.
       XnetNet       pcpu = 1
       XnetNet       pcpu = 3
       XnetNet       pcpu = 2
       XnetNet       pcpu = 3
       XnetNet       pcpu = 7
       XnetNet       pcpu = 0
       XnetNet       pcpu = 5
       XnetNet       pcpu = 3
       XnetNet       pcpu = 0
       XnetNet       pcpu = 3
       XnetNet       pcpu = 7
       XnetNet       pcpu = 4
       XnetNet       pcpu = 5
       XnetNet       pcpu = 2
       XnetNet       pcpu = 4
       XnetNet       pcpu = 5
       XnetNet       pcpu = 6
       XnetNet       pcpu = 0
       XnetNet       pcpu = 6
     
       2) KeSetTargetProcessorDpc(&xi->rx_dpc, 0) is *NOT*commentted.
       XnetNet       pcpu = 0
       XnetNet       pcpu = 0
       XnetNet       pcpu = 0
       XnetNet       pcpu = 0
       XnetNet       pcpu = 0
       XnetNet       pcpu = 0
       XnetNet       pcpu = 0
       XnetNet       pcpu = 0
       XnetNet       pcpu = 0
       XnetNet       pcpu = 0
       XnetNet       pcpu = 0
==================================================

static VOID
XenNet_RxBufferCheck(PKDPC dpc, PVOID context, PVOID arg1, PVOID arg2)
{
  struct xennet_info *xi = context;
  RING_IDX cons, prod;
  LIST_ENTRY rx_packet_list;
  PLIST_ENTRY entry;
  PNDIS_PACKET packets[MAXIMUM_PACKETS_PER_INDICATE];
  ULONG packet_count = 0;
  struct netif_rx_response *rxrsp = NULL;
  struct netif_extra_info *ei;
  USHORT id;
  int more_to_do = FALSE;
  packet_info_t *pi = &xi->rxpi;
  //NDIS_STATUS status;
 &nb sp;shared_buffer_t *page_buf;
  PNDIS_BUFFER buffer;
  ULONG pcpu = KeGetCurrentProcessorNumber() & 0xff;

  UNREFERENCED_PARAMETER(dpc);
  UNREFERENCED_PARAMETER(arg1);
  UNREFERENCED_PARAMETER(arg2);

  //FUNCTION_ENTER();

  KdPrint((__DRIVER_NAME "    pcpu = %lu\n", pcpu));    

  if (!xi->connected)

 
> Subject: RE: Rather slow time of Pin in Windows with GPL PV driver
> Date: Wed, 9 Mar 2011 22:28:48 +1100
> From: james.harper@xxxxxxxxxxxxxxxx
> To: tinnycloud@xxxxxxxxxxx
> CC: xen-devel@xxxxxxxxxxxxxxxxxxx
>
> > I may try pin later, my host has 4 * 4 core CPU.
> >
> > Well, I just compare GPL and RHEL PV driver codes, I noticed most of
> the net
> > driver
> > initialization is the same. Only one difference, in GPL code has the
> code of
> > KeSetTargetProcessorDpc(&xi->rx_dpc, 0); //in xennet_rx.c line 953
> > but the RHEL doesn't
> >
> > So I simply comments the code, recompile and did the test again.
> > The result shows good, all ping time less than < 1ms.
> >
> > May it be the cause? Is it harmful to comments this line?
> > Many thanks.
> >
>
> At a guess I would say it should be harmful to performance, but all the
> critical code is protected by spinlocks.
>
> It could be a leftover from a previous version of GPLPV. In the current
> version, the spinlock protected code is probably a little long winded
> but is nothing compared to the passing down of packets to Windows that
> is done in the DPC but outside the spinlock.
>
> Can you do some general performance tests with this change?
>
> Is the RHEL PV driver source publicly available?
>
> James

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