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([2001:b07:6468:f312:9af8:e5f5:7516:fa89]) by smtp.googlemail.com with ESMTPSA id w7-20020a5d4047000000b003063772a55bsm9426660wrp.61.2023.06.27.00.00.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 Jun 2023 00:00:27 -0700 (PDT) Message-ID: <8edd4b7f-5c6b-db99-a838-484cb49bcb27@redhat.com> Date: Tue, 27 Jun 2023 09:00:26 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH] icount: don't adjust virtual time backwards after warp To: Nicholas Piggin Cc: qemu-devel@nongnu.org, qemu-stable References: <20230627061406.241847-1-npiggin@gmail.com> Content-Language: en-US From: Paolo Bonzini In-Reply-To: <20230627061406.241847-1-npiggin@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 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, NICE_REPLY_A=-0.09, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 6/27/23 08:14, Nicholas Piggin wrote: > The icount-based QEMU_CLOCK_VIRTUAL runs ahead of the RT clock at times. > When warping, it is possible it is still ahead at the end of the warp, > which causes icount adaptive mode to adjust it backward. This can result > in the machine observing time going backwards. > > Prevent this by clamping adaptive adjustment to 0 at minimum. Queued, thanks. Paolo > Signed-off-by: Nicholas Piggin > --- > softmmu/icount.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/softmmu/icount.c b/softmmu/icount.c > index 4504433e16..486ea7ef41 100644 > --- a/softmmu/icount.c > +++ b/softmmu/icount.c > @@ -259,11 +259,16 @@ static void icount_warp_rt(void) > warp_delta = clock - timers_state.vm_clock_warp_start; > if (icount_enabled() == 2) { > /* > - * In adaptive mode, do not let QEMU_CLOCK_VIRTUAL run too > - * far ahead of real time. > + * In adaptive mode, do not let QEMU_CLOCK_VIRTUAL run too far > + * ahead of real time (it might already be ahead so careful not > + * to go backwards). > */ > int64_t cur_icount = icount_get_locked(); > int64_t delta = clock - cur_icount; > + > + if (delta < 0) { > + delta = 0; > + } > warp_delta = MIN(warp_delta, delta); > } > qatomic_set_i64(&timers_state.qemu_icount_bias,