From: Paolo Bonzini <pbonzini@redhat.com>
To: Pavel Dovgaluk <Pavel.Dovgaluk@ispras.ru>,
rth7680@gmail.com, leon.alrae@imgtec.com, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v2 0/3] Fix exceptions handling for MIPS and i386
Date: Thu, 18 Jun 2015 12:02:11 +0200 [thread overview]
Message-ID: <55829723.60009@redhat.com> (raw)
In-Reply-To: <20150618094254.GE3379@aurel32.net>
On 18/06/2015 11:42, Aurelien Jarno wrote:
>> > QEMU could just always compute and store the restore_state information.
>> > TCG needs to help filling it in (a new TCG opcode?), but it should be easy.
> Yes, that was another approach I have in mind (I called it exception
> table in my other mail),
Okay, understood. My idea was more like always generating the gen_op_*
arrays.
> but it requires a tiny more work than just
> saving the CPU state all the time. The problem is that the state
> information we want to save are varying for target to target. Going
> through a TCG opcode means we can use the liveness analysis pass to save
> the minimum amount of data.
I mentioned a TCG opcode because the target PC is not available inside
the translator. So the translator could pepper the TCG instruction
stream with things like
checkpoint $target_pc, $target_cc_op, $0
TCG can then use them to fill in an array stored inside the
TranslationBlock, together with the host PC. Since the gen_opc_pc,
gen_opc_instr_start, gen_opc_icount arrays are inside tcg_ctx, it may be
a good idea to store the checkpoint information compressed in a byte
array (e.g. as a series of ULEB128 values---the host and target PCs can
even be stored as deltas from the last value).
As a first step, gen_intermediate_code_pc and tcg_gen_code_search_pc can
then be merged into a single target-independent function that
uncompresses the byte array up to the required host PC into tcg_ctx.
Later you can optimize them to remove the tcg_ctx arrays altogether.
So the patches could be something like this:
1) SPARC: put the jump target information directly in gen_opc_* without
using gen_opc_jump_pc (not trivial)
2) a few targets: instead of gen_opc_* arrays, use a new generic member
of tcg_ctx (similar to how csbase is used generically), e.g.
tcg_ctx.gen_opc_target1[] and tcg_ctx.gen_opc_target2[].
3) all targets: always fill in tcg_ctx.gen_*, even if search_pc is false
4) TCG: add support for a checkpoint operation, make it fill in
tcg_ctx.gen_*
5) all targets: change explicit filling of tcg_ctx.gen_* to use the
checkpoint operation
6) TCG/translate-all: convert gen_intermediate_code_pc as outlined above
> That said I would like to push further the idea of always saving the CPU
> state a bit more to see if we can keep the same performances. There are
> still improvements to do, by removing more code on the core side (like
> finding the call to tb_finc_pc which is now useless), or on the target
> side by checking/improving helper flags. We might save the CPU state too
> often if a helper doesn't declare it doesn't touch globals.
True, on the other hand there are a lot of helpers to audit...
Paolo
next prev parent reply other threads:[~2015-06-18 10:02 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-17 12:41 [Qemu-devel] [PATCH v2 0/3] Fix exceptions handling for MIPS and i386 Pavel Dovgalyuk
2015-06-17 12:42 ` [Qemu-devel] [PATCH v2 1/3] softmmu: add helper function to pass through retaddr Pavel Dovgalyuk
2015-06-17 12:53 ` Paolo Bonzini
2015-06-18 5:17 ` Pavel Dovgaluk
2015-06-18 8:16 ` Paolo Bonzini
2015-06-18 8:20 ` Aurelien Jarno
2015-06-18 9:24 ` Pavel Dovgaluk
2015-06-18 9:30 ` Paolo Bonzini
2015-06-18 9:33 ` Pavel Dovgaluk
2015-06-18 9:35 ` Paolo Bonzini
2015-06-17 12:42 ` [Qemu-devel] [PATCH v2 2/3] target-mips: exceptions handling in icount mode Pavel Dovgalyuk
2015-06-17 13:05 ` Aurelien Jarno
2015-06-17 12:42 ` [Qemu-devel] [PATCH v2 3/3] target-i386: fix memory operations in helpers Pavel Dovgalyuk
2015-06-17 13:27 ` Aurelien Jarno
2015-06-17 13:24 ` [Qemu-devel] [PATCH v2 0/3] Fix exceptions handling for MIPS and i386 Aurelien Jarno
2015-06-18 6:18 ` Pavel Dovgaluk
2015-06-17 14:19 ` Aurelien Jarno
2015-06-18 7:12 ` Pavel Dovgaluk
2015-06-18 8:16 ` Aurelien Jarno
2015-06-18 8:58 ` Pavel Dovgaluk
2015-06-18 9:08 ` Aurelien Jarno
2015-06-18 9:29 ` Paolo Bonzini
2015-06-18 9:42 ` Aurelien Jarno
2015-06-18 10:02 ` Paolo Bonzini [this message]
2015-06-18 17:42 ` Aurelien Jarno
2015-06-19 5:09 ` Pavel Dovgaluk
2015-06-19 8:22 ` Aurelien Jarno
[not found] ` <55826f70.2215370a.4634.ffff91b2SMTPIN_ADDED_BROKEN@mx.google.com>
2015-06-18 7:51 ` Peter Maydell
2015-06-18 7:56 ` Pavel Dovgaluk
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