From: "Philippe Mathieu-Daudé" <philmd@linaro.org>
To: Richard Henderson <richard.henderson@linaro.org>, qemu-devel@nongnu.org
Subject: Re: [PATCH v3 00/10] accel/tcg: Improve tb_flush usage
Date: Wed, 24 Sep 2025 14:14:16 +0200 [thread overview]
Message-ID: <6ef7e6e1-9ac1-466d-b4bc-332e135c258e@linaro.org> (raw)
In-Reply-To: <20250923215425.3685950-1-richard.henderson@linaro.org>
On 23/9/25 23:54, Richard Henderson wrote:
> It is too easy to mis-use tb_flush(). For instance, because of
> the cpu argument, some parts assumed that it needed to call the
> global flush function for every cpu. It is easy to forget that
> the flush is not complete when the call returns: we have merely
> queued work to the cpu run loop. So: remove tb_flush and expose
> only the core as tb_flush__exclusive, to be used only when we
> are already within an exclusive context.
>
> In some cases (gdbstub, alpha, riscv, ppc spapr),
> we can eliminate the need for tb_flush completely.
>
> Changes for v3:
> - Rename to tb_flush__exclusive_or_serial; retain the serial
> check within, not updating to exclusive only.
> - Rename the existing tb_flush to queue_tb_flush; retain the
> sequence number check for duplicated flushes.
> - Drop EXCP_TB_FLUSH.
When using my split-accel branch, I had good results with v2.
I'm getting crashes with v3:
Termination Reason: Namespace SIGNAL, Code 4 Illegal instruction: 4
Thread 4 Crashed:
0 ??? 0x34400fb00 ???
1 qemu-system-aarch64-unsigned 0x100fd74dc cpu_tb_exec + 160 (cpu-exec.c:441)
2 qemu-system-aarch64-unsigned 0x100fd829c cpu_loop_exec_tb + 32 (cpu-exec.c:897) [inlined]
3 qemu-system-aarch64-unsigned 0x100fd829c cpu_exec_loop + 904 (cpu-exec.c:1009)
4 qemu-system-aarch64-unsigned 0x100fd7a30 cpu_exec_setjmp + 48 (cpu-exec.c:1026)
5 qemu-system-aarch64-unsigned 0x100fd7954 cpu_exec + 496 (cpu-exec.c:1052)
6 qemu-system-aarch64-unsigned 0x100ff9bc4 tcg_cpu_exec + 44 (tcg-accel-ops.c:97)
7 qemu-system-aarch64-unsigned 0x100ffa4c4 mttcg_cpu_exec + 28 (tcg-accel-ops-mttcg.c:146)
8 qemu-system-aarch64-unsigned 0x10140bdac split_cpu_thread_routine + 540 (split-accel-ops.c:87)
9 qemu-system-aarch64-unsigned 0x10158f7e0 qemu_thread_start + 132 (qemu-thread-posix.c:393)
Thread 5:
0 qemu-system-aarch64-unsigned 0x100fb04e0 tcg_out_ld + 160 (tcg-target.c.inc:1268)
1 qemu-system-aarch64-unsigned 0x100fab3f8 tcg_reg_alloc_op + 240 [inlined]
2 qemu-system-aarch64-unsigned 0x100fab3f8 tcg_gen_code + 7932 (tcg.c:7018)
3 qemu-system-aarch64-unsigned 0x100fe9e88 setjmp_gen_code + 184 (translate-all.c:257)
4 qemu-system-aarch64-unsigned 0x100fe9780 tb_gen_code + 364 (translate-all.c:324)
5 qemu-system-aarch64-unsigned 0x100fd8138 cpu_exec_loop + 548 (cpu-exec.c:980)
6 qemu-system-aarch64-unsigned 0x100fd7a30 cpu_exec_setjmp + 48 (cpu-exec.c:1026)
7 qemu-system-aarch64-unsigned 0x100fd7954 cpu_exec + 496 (cpu-exec.c:1052)
8 qemu-system-aarch64-unsigned 0x100ff9bc4 tcg_cpu_exec + 44 (tcg-accel-ops.c:97)
9 qemu-system-aarch64-unsigned 0x100ffa4c4 mttcg_cpu_exec + 28 (tcg-accel-ops-mttcg.c:146)
10 qemu-system-aarch64-unsigned 0x10140bdac split_cpu_thread_routine + 540 (split-accel-ops.c:87)
11 qemu-system-aarch64-unsigned 0x10158f7e0 qemu_thread_start + 132 (qemu-thread-posix.c:393)
next prev parent reply other threads:[~2025-09-24 12:15 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-23 21:54 [PATCH v3 00/10] accel/tcg: Improve tb_flush usage Richard Henderson
2025-09-23 21:54 ` [PATCH v3 01/10] gdbstub: Remove tb_flush uses Richard Henderson
2025-09-23 21:54 ` [PATCH v3 02/10] target/alpha: Simplify call_pal implementation Richard Henderson
2025-09-23 21:54 ` [PATCH v3 03/10] target/riscv: Record misa_ext in TCGTBCPUState.cs_base Richard Henderson
2025-09-23 21:54 ` [PATCH v3 04/10] hw/ppc/spapr: Use tb_invalidate_phys_range in h_page_init Richard Henderson
2025-09-24 3:20 ` Philippe Mathieu-Daudé
2025-09-23 21:54 ` [PATCH v3 05/10] accel/tcg: Split out tb_flush__exclusive_or_serial Richard Henderson
2025-09-25 2:15 ` Philippe Mathieu-Daudé
2025-09-23 21:54 ` [PATCH v3 06/10] accel/tcg: Move post-load tb_flush to vm_change_state hook Richard Henderson
2025-09-23 21:54 ` [PATCH v3 07/10] plugins: Use tb_flush__exclusive_or_serial Richard Henderson
2025-09-23 21:54 ` [PATCH v3 08/10] linux-user: Split out begin_parallel_context Richard Henderson
2025-09-24 3:23 ` Philippe Mathieu-Daudé
2025-09-23 21:54 ` [PATCH v3 09/10] accel/tcg: Create queue_tb_flush from tb_flush Richard Henderson
2025-09-24 3:26 ` Philippe Mathieu-Daudé
2025-09-23 21:54 ` [PATCH v3 10/10] accel/tcg: Improve buffer overflow in tb_gen_code Richard Henderson
2025-09-24 12:14 ` Philippe Mathieu-Daudé [this message]
2025-09-24 16:39 ` [PATCH v3 00/10] accel/tcg: Improve tb_flush usage Richard Henderson
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