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(p200300cbc7496600b73a466ce6100686.dip0.t-ipconnect.de. [2003:cb:c749:6600:b73a:466c:e610:686]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43656b0153asm53314395e9.14.2024.12.19.06.11.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Dec 2024 06:11:48 -0800 (PST) Message-ID: <10d02197-88a7-4aad-afc3-fe9584a5a458@redhat.com> Date: Thu, 19 Dec 2024 15:11:47 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] hw/virtio: reset virtio balloon stats on machine reset To: =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= Cc: qemu-devel@nongnu.org, "Michael S. Tsirkin" References: <20241218172912.4170899-1-berrange@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1.116, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 19.12.24 15:08, Daniel P. Berrangé wrote: > On Thu, Dec 19, 2024 at 02:51:21PM +0100, David Hildenbrand wrote: >> On 18.12.24 18:29, Daniel P. Berrangé wrote: >>> When a machine is first booted, all virtio balloon stats are initialized >>> to their default value -1 (18446744073709551615 when represented as >>> unsigned). >>> >>> They remain that way while the firmware is loading, and early phase of >>> guest OS boot, until the virtio-balloon driver is activated. Thereafter >>> the reported stats reflect the guest OS activity. >>> >>> When a machine reset is performed, however, the virtio-balloon stats are >>> left unchanged by QEMU, despite the guest OS no longer updating them, >>> nor indeed even still existing. >>> >>> IOW, the mgmt app keeps getting stale stats until the guest OS starts >>> once more and loads the virtio-balloon driver (if ever). At that point >>> the app will see a discontinuity in the reported values as they sudden >>> jump from the stale value to the new value. This jump is indigituishable >>> from a valid data update. >>> >>> While there is an "last-updated" field to report on the freshness of >>> the stats, that does not unambiguously tell the mgmt app whether the >>> stats are still conceptually relevant to the current running workload. >>> >>> It is more conceptually useful to reset the stats to their default >>> values on machine reset, given that the previous guest workload the >>> stats reflect no longer exists. The mgmt app can now clearly identify >>> that there are is no stats information available from the current >>> executing workload. >>> >>> The 'last-updated' time is also reset back to 0. >>> >>> IOW, on every machine reset, the virtio stats are in the same clean >>> state they were when the macine first powered on. >>> >>> A functional test is added to validate this behaviour with a real >>> world guest OS. >>>> Signed-off-by: Daniel P. Berrangé >>> --- >>> >>> One side-thought I have, is whether it makes sense to add a >>> 'reset-count' field in the virtio stats, alongside the >>> 'last-updated' field. While apps can infer a reset from seeing >>> the stats all go back to their defaults, an explicit flag is >>> simpler... >>> >>> MAINTAINERS | 1 + >>> hw/virtio/virtio-balloon.c | 30 ++++- >>> include/hw/virtio/virtio-balloon.h | 4 + >>> tests/functional/test_virtio_balloon.py | 161 ++++++++++++++++++++++++ >>> 4 files changed, 195 insertions(+), 1 deletion(-) >>> create mode 100755 tests/functional/test_virtio_balloon.py >>> >>> diff --git a/MAINTAINERS b/MAINTAINERS >>> index 822f34344b..1380d53d03 100644 >>> --- a/MAINTAINERS >>> +++ b/MAINTAINERS >>> @@ -2234,6 +2234,7 @@ F: include/hw/virtio/virtio-balloon.h >>> F: system/balloon.c >>> F: include/sysemu/balloon.h >>> F: tests/qtest/virtio-balloon-test.c >>> +F: tests/functional/test_virtio_balloon.py >>> virtio-9p >>> M: Greg Kurz >>> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c >>> index ab2ee30475..fe0854e198 100644 >>> --- a/hw/virtio/virtio-balloon.c >>> +++ b/hw/virtio/virtio-balloon.c >>> @@ -31,7 +31,7 @@ >>> #include "trace.h" >>> #include "qemu/error-report.h" >>> #include "migration/misc.h" >>> - >>> +#include "sysemu/reset.h" >>> #include "hw/virtio/virtio-bus.h" >>> #include "hw/virtio/virtio-access.h" >>> @@ -910,6 +910,8 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp) >>> } >>> reset_stats(s); >>> + s->stats_last_update = 0; >>> + qemu_register_resettable(OBJECT(dev)); >>> } >>> static void virtio_balloon_device_unrealize(DeviceState *dev) >>> @@ -917,6 +919,7 @@ static void virtio_balloon_device_unrealize(DeviceState *dev) >>> VirtIODevice *vdev = VIRTIO_DEVICE(dev); >>> VirtIOBalloon *s = VIRTIO_BALLOON(dev); >>> + qemu_unregister_resettable(OBJECT(dev)); >>> if (s->free_page_bh) { >>> qemu_bh_delete(s->free_page_bh); >>> object_unref(OBJECT(s->iothread)); >>> @@ -987,6 +990,27 @@ static void virtio_balloon_set_status(VirtIODevice *vdev, uint8_t status) >>> } >>> } >> >> Using qemu_register_resettable() can have unfortunate side effects that this >> code is triggered when the device is reset, not necessarily when the >> complete machine. >> >> For virtio-mem at least that's an issue, and here is how I'll fix it: >> >> https://lore.kernel.org/qemu-devel/20241218105303.1966303-2-david@redhat.com/ > > Urgh, that's a rather horrible situation. While your patch works around > it quite effectively, it is pretty heavy weight, and of course relies on > maintainers knowing this scenario exists - they won't learn this easily > from the Resettable API design, nor its docs :-( Yes. > > Shouldn't we put to extend the Resettable design to make this scenario > more explicity distinguishable in the Resettable callback implementations. I'd be happy if I wouldn't need that heavy-weight stuff in virtio-mem code as well, so if you have ideas on how to avoid that in the future, that'd be great. -- Cheers, David / dhildenb