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Wed, 2 Oct 2019 18:19:06 +0000 (UTC) Received: from [10.36.116.21] (ovpn-116-21.ams2.redhat.com [10.36.116.21]) by smtp.corp.redhat.com (Postfix) with ESMTP id 48A62608C0; Wed, 2 Oct 2019 18:19:05 +0000 (UTC) Subject: Re: [PATCH v2] s390x/tcg: MVCL: Exit to main loop if requested To: Richard Henderson , =?UTF-8?Q?Alex_Benn=c3=a9e?= , qemu-devel@nongnu.org References: <20191002082636.7739-1-david@redhat.com> <87zhijjwph.fsf@linaro.org> <0479ad1f-348e-ed40-c2c6-aef168afdb7e@linaro.org> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwX4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEE3eEPcA/4Na5IIP/3T/FIQMxIfNzZshIq687qgG 8UbspuE/YSUDdv7r5szYTK6KPTlqN8NAcSfheywbuYD9A4ZeSBWD3/NAVUdrCaRP2IvFyELj xoMvfJccbq45BxzgEspg/bVahNbyuBpLBVjVWwRtFCUEXkyazksSv8pdTMAs9IucChvFmmq3 jJ2vlaz9lYt/lxN246fIVceckPMiUveimngvXZw21VOAhfQ+/sofXF8JCFv2mFcBDoa7eYob s0FLpmqFaeNRHAlzMWgSsP80qx5nWWEvRLdKWi533N2vC/EyunN3HcBwVrXH4hxRBMco3jvM m8VKLKao9wKj82qSivUnkPIwsAGNPdFoPbgghCQiBjBe6A75Z2xHFrzo7t1jg7nQfIyNC7ez MZBJ59sqA9EDMEJPlLNIeJmqslXPjmMFnE7Mby/+335WJYDulsRybN+W5rLT5aMvhC6x6POK z55fMNKrMASCzBJum2Fwjf/VnuGRYkhKCqqZ8gJ3OvmR50tInDV2jZ1DQgc3i550T5JDpToh dPBxZocIhzg+MBSRDXcJmHOx/7nQm3iQ6iLuwmXsRC6f5FbFefk9EjuTKcLMvBsEx+2DEx0E UnmJ4hVg7u1PQ+2Oy+Lh/opK/BDiqlQ8Pz2jiXv5xkECvr/3Sv59hlOCZMOaiLTTjtOIU7Tq 7ut6OL64oAq+zsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/CA/lc/LMthqQ773ga uB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseBfDXHA6m4B3mUTWo13nid 0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X 2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+ xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC 8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvFFFyAS0Nk1q/7EChPcbRb hJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkC u8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRkF3TwgucpyPtcpmQtTkWS gDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0LLH63+BrrHasfJzxKXzqg rW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABwsFl BBgBAgAPBQJVy5+RAhsMBQkJZgGAAAoJEE3eEPcA/4NagOsP/jPoIBb/iXVbM+fmSHOjEshl KMwEl/m5iLj3iHnHPVLBUWrXPdS7iQijJA/VLxjnFknhaS60hkUNWexDMxVVP/6lbOrs4bDZ NEWDMktAeqJaFtxackPszlcpRVkAs6Msn9tu8hlvB517pyUgvuD7ZS9gGOMmYwFQDyytpepo YApVV00P0u3AaE0Cj/o71STqGJKZxcVhPaZ+LR+UCBZOyKfEyq+ZN311VpOJZ1IvTExf+S/5 lqnciDtbO3I4Wq0ArLX1gs1q1XlXLaVaA3yVqeC8E7kOchDNinD3hJS4OX0e1gdsx/e6COvy qNg5aL5n0Kl4fcVqM0LdIhsubVs4eiNCa5XMSYpXmVi3HAuFyg9dN+x8thSwI836FoMASwOl C7tHsTjnSGufB+D7F7ZBT61BffNBBIm1KdMxcxqLUVXpBQHHlGkbwI+3Ye+nE6HmZH7IwLwV W+Ajl7oYF+jeKaH4DZFtgLYGLtZ1LDwKPjX7VAsa4Yx7S5+EBAaZGxK510MjIx6SGrZWBrrV TEvdV00F2MnQoeXKzD7O4WFbL55hhyGgfWTHwZ457iN9SgYi1JLPqWkZB0JRXIEtjd4JEQcx +8Umfre0Xt4713VxMygW0PnQt5aSQdMD58jHFxTk092mU+yIHj5LeYgvwSgZN4airXk5yRXl SE+xAvmumFBY Organization: Red Hat GmbH Message-ID: <271321d9-e43b-7a84-341b-17eb91972ada@redhat.com> Date: Wed, 2 Oct 2019 20:19:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <0479ad1f-348e-ed40-c2c6-aef168afdb7e@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Wed, 02 Oct 2019 18:19:06 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-s390x@nongnu.org, Cornelia Huck , Thomas Huth Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 02.10.19 18:47, Richard Henderson wrote: > On 10/2/19 2:58 AM, Alex Benn=C3=A9e wrote: >> >> David Hildenbrand writes: >> >>> MVCL is interruptible and we should check for interrupts and process >>> them after writing back the variables to the registers. Let's check >>> for any exit requests and exit to the main loop. >>> >>> When booting Fedora 30, I can see a handful of these exits and it see= ms >>> to work reliable. (it never get's triggered via EXECUTE, though) >>> >>> Suggested-by: Richard Henderson >>> Signed-off-by: David Hildenbrand >>> --- >>> >>> v1 -> v2: >>> - Check only if icount_decr.u32 < 0 >>> - Drop should_interrupt_instruction() and perform the check inline >>> - Rephrase comment, subject, and description >>> >>> --- >>> target/s390x/mem_helper.c | 10 +++++++++- >>> 1 file changed, 9 insertions(+), 1 deletion(-) >>> >>> diff --git a/target/s390x/mem_helper.c b/target/s390x/mem_helper.c >>> index 4254548935..87e4ebd169 100644 >>> --- a/target/s390x/mem_helper.c >>> +++ b/target/s390x/mem_helper.c >>> @@ -1015,6 +1015,7 @@ uint32_t HELPER(mvcl)(CPUS390XState *env, uint3= 2_t r1, uint32_t r2) >>> uint64_t srclen =3D env->regs[r2 + 1] & 0xffffff; >>> uint64_t src =3D get_address(env, r2); >>> uint8_t pad =3D env->regs[r2 + 1] >> 24; >>> + CPUState *cs =3D env_cpu(env); >>> S390Access srca, desta; >>> uint32_t cc, cur_len; >>> >>> @@ -1065,7 +1066,14 @@ uint32_t HELPER(mvcl)(CPUS390XState *env, uint= 32_t r1, uint32_t r2) >>> env->regs[r1 + 1] =3D deposit64(env->regs[r1 + 1], 0, 24, de= stlen); >>> set_address_zero(env, r1, dest); >>> >>> - /* TODO: Deliver interrupts. */ >>> + /* >>> + * MVCL is interruptible. Check if somebody (e.g., cpu_inter= rupt() or >>> + * cpu_exit()) asked us to return to the main loop. In case = there is >>> + * no deliverable interrupt, we'll end up back in this handl= er. >>> + */ >>> + if >>> (unlikely((int32_t)atomic_read(&cpu_neg(cs)->icount_decr.u32) < 0)) { >> >> I'm not sure about directly checking the icount_decr here. It really i= s >> an internal implementation detail for the generated code. >=20 > But it's also the exact right thing to test. >=20 >=20 >> Having said >> that is seems cpu_interrupt() is messing with this directly rather tha= n >> calling cpu_exit() which sets the more easily checked &cpu->exit_reque= st. >> >> This is potentially problematic as in other points in the cpu loop cod= e >> you see checks like this: >> >> /* Finally, check if we need to exit to the main loop. */ >> if (unlikely(atomic_read(&cpu->exit_request)) >> || (use_icount >> && cpu_neg(cpu)->icount_decr.u16.low + cpu->icount_extra =3D= =3D 0)) { >> atomic_set(&cpu->exit_request, 0); >> if (cpu->exception_index =3D=3D -1) { >> cpu->exception_index =3D EXCP_INTERRUPT; >> } >> return true; >> } >> >> although I guess this is because interrupts and "exits" take subtly >> different paths through the outer loop. Given that exits and interrupt= s >> are slightly different is what you want to check >> atomic_read(&cpu->interrupt_request))? >=20 > No, this is not about interrupts per se. >=20 > The thing we're trying to solve here is MVCL running for a long time. = The > length operand is 24 bits, so max 16MB can be copied with one instructi= on. We > want to exit back to the main loop early when told to do so, as the ins= n is > officially restartable. >=20 > Ordinarily, I would say move the loop out to the tcg level, but that cr= eates > further complications and I'd rather not open up that can of worms. While that is feasible, I agree that it's not the simplest approach. >=20 > There is still the special case of EXECUTE of MVCL, which I suspect mus= t have > some failure mode that we're not considering -- the setting and clearin= g of > ex_value can't help. I have a suspicion that we need to special case t= hat > within helper_ex, just so that ex_value doesn't enter into it. We could rap that in something like cpu_cond_loop_exit_restore() inspired by cond_resched() in the kernel. Then, at least the implementation specifics are kept where they actually belong. --=20 Thanks, David / dhildenb