Re: 5.0.0-rc3 : Opcode 1f 12 0f 00 (7ce003e4) leaked temporaries

[Cédric Le Goater]

On 4/17/20 1:14 PM, Peter Maydell wrote:
> On Fri, 17 Apr 2020 at 12:00, BALATON Zoltan <address@hidden> wrote:
>> On Fri, 17 Apr 2020, Peter Maydell wrote:
>>> And yes, debug
>>> is slower (it builds QEMU without optimization enabled
>>> so it's easier to debug QEMU in gdb, and it turns on
>>> various extra sanity checks.)
>>
>> Last time I've looked I've found it effectively disables TB cache (at
>> least with PPC) because one of those checks forces a flush which is the
>> main source of the slowness with --enable-debug. Not sure if this could be
>> avoided, I didn't know about --disable-tcg-debug Philippe suggested so
>> haven't tested that.
> 
> It's not supposed to disable TB caching, and in my experience
> it does not (no TB caching at all is incredibly slow). If it's
> doing that on PPC that would be worth investigating.
> 
> I do almost all of my work and local testing with --enable-debug,
> so I notice if it's slowed down to the extent that "no TB caching"
> would involve. It is naturally slower than the non-debug config
> both because of some extra checking and also because all the C
> code is being compiled at -O0 rather than -O2.

Booting a pseries machine (kernel/initrd) with --enable-debug is
about 2.5 x slower.

C.