linux-kernel - [PATCH 0/3] XICS emulation optimizations in KVM for PPC

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Date: Mon,  6 May 2024 21:47:28 +0530
From: Gautam Menghani <gautam@...ux.ibm.com>
To: mpe@...erman.id.au, npiggin@...il.com, christophe.leroy@...roup.eu,
        naveen.n.rao@...ux.ibm.com
Cc: Gautam Menghani <gautam@...ux.ibm.com>, linuxppc-dev@...ts.ozlabs.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 0/3] XICS emulation optimizations in KVM for PPC

Optimize the XICS emulation code in KVM as per the 'performance todos'
in the comments of book3s_xics.c. 

Performance numbers:
1. Test case: Pgbench run in a KVM on PowerVM guest for 120 secs


2. Time taken by arch_send_call_function_single_ipi() currently measured 
with funclatency [1].

$ ./funclatency.py -u arch_send_call_function_single_ipi

usecs               : count     distribution
0 -> 1          : 7        |                                        |
2 -> 3          : 16       |                                        |
4 -> 7          : 141      |                                        |
8 -> 15         : 4455631  |****************************************|
16 -> 31         : 437981   |***                                     |
32 -> 63         : 5036     |                                        |
64 -> 127        : 92       |                                        |

avg = 12 usecs, total: 60,532,481 usecs, count: 4,898,904


3. Time taken by arch_send_call_function_single_ipi() with changes in
this series.

$ ./funclatency.py -u arch_send_call_function_single_ipi

usecs               : count     distribution
0 -> 1          : 15       |                                        |
2 -> 3          : 7        |                                        |
4 -> 7          : 3798     |                                        |
8 -> 15         : 4569610  |****************************************|
16 -> 31         : 339284   |**                                      |
32 -> 63         : 4542     |                                        |
64 -> 127        : 68       |                                        |
128 -> 255        : 0        |                                        |
256 -> 511        : 1        |                                        |

avg = 11 usecs, total: 57,720,612 usecs, count: 4,917,325

4. This patch series has been also tested on KVM on Power8 CPU.

[1]: https://github.com/iovisor/bcc/blob/master/tools/funclatency.py

Gautam Menghani (3):
  arch/powerpc/kvm: Use bitmap to speed up resend of irqs in ICS
  arch/powerpc/kvm: Optimize the server number -> ICP lookup
  arch/powerpc/kvm: Reduce lock contention by moving spinlock from ics
    to irq_state

 arch/powerpc/kvm/book3s_hv_rm_xics.c |  8 ++--
 arch/powerpc/kvm/book3s_xics.c       | 70 ++++++++++++----------------
 arch/powerpc/kvm/book3s_xics.h       | 13 ++----
 3 files changed, 39 insertions(+), 52 deletions(-)

-- 
2.44.0