Re: [PATCH 0/1] KVM: x86: improve the usability of the 'kvm_pio' tracepoint

[Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>]

On 05/02/2014 11:57 PM, Ulrich Obergfell wrote:
> The current implementation of the 'kvm_pio' tracepoint in emulator_pio_in_out()
> only tells us that 'something' has been read from or written to an I/O port. To
> improve the usability of the tracepoint, I propose to include the value/content
> that has been read or written in the trace output. The proposed patch aims at
> the more common case where a single 8-bit or 16-bit or 32-bit value has been
> read or written -- it does not fully cover the case where 'count' is greater
> than one.
> 
> This is an example of what the patch can do (trace of PCI config space access).
> 
>  - on the host
> 
>    # trace-cmd record -e kvm:kvm_pio -f "(port >= 0xcf8) && (port <= 0xcff)"
>    /sys/kernel/debug/tracing/events/kvm/kvm_pio/filter
>    Hit Ctrl^C to stop recording
> 
>  - in a Linux guest
> 
>    # dd if=/sys/bus/pci/devices/0000:00:06.0/config bs=2 count=4 | hexdump
>    4+0 records in
>    4+0 records out
>    8 bytes (8 B) copied, 0.000114056 s, 70.1 kB/s
>    0000000 1af4 1001 0507 0010                    
>    0000008
> 
>  - on the host
> 
>    # trace-cmd report
>    ...
>            qemu-kvm-23216 [001] 15211.994089: kvm_pio:              pio_write
>    at 0xcf8 size 4 count 1 val 0x80003000 
>            qemu-kvm-23216 [001] 15211.994108: kvm_pio:              pio_read
>    at 0xcfc size 2 count 1 val 0x1af4 
>            qemu-kvm-23216 [001] 15211.994129: kvm_pio:              pio_write
>    at 0xcf8 size 4 count 1 val 0x80003000 
>            qemu-kvm-23216 [001] 15211.994136: kvm_pio:              pio_read
>    at 0xcfe size 2 count 1 val 0x1001 
>            qemu-kvm-23216 [001] 15211.994143: kvm_pio:              pio_write
>    at 0xcf8 size 4 count 1 val 0x80003004 
>            qemu-kvm-23216 [001] 15211.994150: kvm_pio:              pio_read
>    at 0xcfc size 2 count 1 val 0x507 
>            qemu-kvm-23216 [001] 15211.994155: kvm_pio:              pio_write
>    at 0xcf8 size 4 count 1 val 0x80003004 
>            qemu-kvm-23216 [001] 15211.994161: kvm_pio:              pio_read
>    at 0xcfe size 2 count 1 val 0x10 
> 

Nice.

Could please check "perf kvm stat" to see if "--event=ioport"
can work after your patch?

Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>