From: "Alex Bennée" <1896298@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Bug 1896298] Re: [RFC PATCH] accel/tcg: change default codegen buffer size for i386-softmmu
Date: Fri, 04 Jun 2021 07:42:42 -0000 [thread overview]
Message-ID: <87o8cm6oxe.fsf@linaro.org> (raw)
Message-ID: <20210604074242.YSnxTVaUOSvvlVhNQA4OX8ANtYCOzWKCAHuoirSXLTo@z> (raw)
In-Reply-To: 160046874518.13612.4861858859499751315.malonedeb@gac.canonical.com
Richard Henderson <richard.henderson@linaro.org> writes:
> On 5/25/21 9:45 AM, Alex Bennée wrote:
>> There are two justifications for making this change. The first is that
>> i386 emulation is typically for smaller machines where having a 1gb of
>> generated code is overkill for basic emulation. The second is the
>> propensity of self-modifying code (c.f. Doom/edit) utilised on i386
>> systems can trigger a rapid growth in invalidated and re-translated
>> buffers. This is seen in bug #283. Execution is still inefficient but
>> at least the host memory isn't so aggressively used up.
>> That said it's still really just a sticking plaster for user
>> convenience.
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>> Cc: Thomas Huth <thuth@redhat.com>
>> Cc: 1896298@bugs.launchpad.net
>> ---
>> accel/tcg/translate-all.c | 4 ++++
>> 1 file changed, 4 insertions(+)
>> diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c
>> index 640ff6e3e7..f442165674 100644
>> --- a/accel/tcg/translate-all.c
>> +++ b/accel/tcg/translate-all.c
>> @@ -951,9 +951,13 @@ static void page_lock_pair(PageDesc **ret_p1, tb_page_addr_t phys1,
>> * Users running large scale system emulation may want to tweak their
>> * runtime setup via the tb-size control on the command line.
>> */
>> +#ifdef TARGET_I386
>> +#define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (32 * MiB)
>> +#else
>> #define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (1 * GiB)
>> #endif
>> #endif
>> +#endif
>> #define DEFAULT_CODE_GEN_BUFFER_SIZE \
>> (DEFAULT_CODE_GEN_BUFFER_SIZE_1 < MAX_CODE_GEN_BUFFER_SIZE \
>>
>
> I'm not thrilled, as it is ultra-hacky.
I don't disagree.
> (1) I've got a re-org of this code out for review:
> https://patchew.org/QEMU/20210502231844.1977630-1-richard.henderson@linaro.org/
OK I'll have a look at that.
> (2) I'm keen to reorg TCG such that it gets compiled once. There's
> currently nothing standing in the way of that except work. But this
> would introduce a use of a target-specific define for the first time
> into tcg/. I guess I could leave the default sizing back in
> accel/tcg/ and pass in the default.
>
> Other options?
Some random thoughts in no particular order:
- a separately flushable translation region for code we detect as SMC
heavy
- a front-end interpreter for SMC code
- smarter code generation that dynamically loads values from codemem
(usually the SMC code is just tweaking an #imm value)
None of these seem particularly amenable to a clean non-complex
implementation though. A front-end interpreter would be useful for other
things though - it could even be incomplete and handle only common code
patterns falling back to full generation for anything it can't handle.
>
>
> r~
--
Alex Bennée
--
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1896298
Title:
TCG memory leak with FreeDOS 'edit'
Status in QEMU:
Expired
Bug description:
qemu trunk as of today leaks memory FAST when freedos' edit is
running.
To reproduce, download:
https://www.ibiblio.org/pub/micro/pc-
stuff/freedos/files/repositories/1.3/cdrom.iso
Then run:
$ qemu-system-i386 -cdrom cdrom.iso
select your language then select "return to DOS", then type
> edit
it will consume memory at ~10MB/s
This does NOT happen when adding -enable-kvm
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1896298/+subscriptions
next prev parent reply other threads:[~2021-06-04 8:12 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-18 22:39 [Bug 1896298] [NEW] memory leak Michael Slade
2020-09-18 23:20 ` [Bug 1896298] " Michael Slade
2020-12-02 7:55 ` Thomas Huth
2021-05-11 13:35 ` Thomas Huth
2021-05-13 12:16 ` [Bug 1896298] Re: TCG memory leak with FreeDOS 'edit' Thomas Huth
2021-05-25 14:51 ` Alex Bennée
2021-05-25 16:45 ` [Bug 1896298] [RFC PATCH] accel/tcg: change default codegen buffer size for i386-softmmu Alex Bennée
2021-05-25 16:45 ` Alex Bennée
2021-06-03 16:33 ` Alex Bennée
2021-06-03 16:33 ` [Bug 1896298] " Alex Bennée
2021-06-03 19:04 ` Richard Henderson
2021-06-04 7:42 ` Alex Bennée [this message]
2021-06-04 7:42 ` [Bug 1896298] " Alex Bennée
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