From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oi1-f201.google.com (mail-oi1-f201.google.com [209.85.167.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7CE5D201113 for ; Tue, 3 Mar 2026 00:26:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.167.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772497618; cv=none; b=J6AmWGvEoywEcnzjmu2Ugnp/v5d+7UfU+muO1rwKuEh5MvncFJ3/89njr6MqVo/PWy8jwrKI9WCkTqZ8/U4ZT/vHgKCsW/Vdzj+SY981vjfbDXeG5paoQlh9PJH5OEuCNFmQlRyqUfXIKvuCKs6TL6KEE70qzK1uv94q8oLzg7M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772497618; c=relaxed/simple; bh=45FwaD+aLfwCpOLp1QzR80s2bnH1PdYm5y06Mq7rG5M=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=seos7kDWXEE8LFjWd4ylhFaNgPW7f6Y/lwWV+tLX0u9uEKefQuxhnA4brGwlIhZ4muM8DVzww2injgwZsqIdpszgFuQSLWPW0b2I2nycw5s20xltQ+R3XDkJwpJzgPh0WDgV5ebLnwAjQt67LGAVhnXrrJSdD5gT94HasWJz5Sc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=y/9POyzw; arc=none smtp.client-ip=209.85.167.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="y/9POyzw" Received: by mail-oi1-f201.google.com with SMTP id 5614622812f47-463a075e177so26757819b6e.2 for ; Mon, 02 Mar 2026 16:26:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1772497616; x=1773102416; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:from:to:cc:subject:date:message-id :reply-to; bh=x4ktjRaCV60il5GnKrl3u+MiHKCG6sTxE87cgQM8iWE=; b=y/9POyzwHlwetQ+M7I0WkuK6acC/pzzq8rN5ORcGLdJaNEltWiSBWYRpYm9Hk8wr2u Fz/LdH2IvlM0S/IsZiP9lGqvQo76tUiPpt+BRoi6CvpR2eIJiWz/+HT1TSPKx2jnHV7i zl1gZeLJTc3Q+qm4qq5Y8aBi8GSzyzEsJaU4ircC21nfzLaryy9v0yYCudeHWUwnTQ1l +XayaXukmQHRRI8VQcZg9+RVyOA1TVRfSExyXFtpPaLGp6pRJ+rVkO6x4duAGG5z+5xA LNeuuB9yKln4hvw495rRacM3LvDBuI8M4l7cqeVfi5lDlPgeBRHuzPaplpe5vlCCrWjp 45Xw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1772497616; x=1773102416; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=x4ktjRaCV60il5GnKrl3u+MiHKCG6sTxE87cgQM8iWE=; b=ENlaktnD/jUIJFGAnmme+22Bm+x2igZNy8Jasbi41Bo6RPIdkjm+okeSVE8UvoYaqf R3T0T70hWwUqpxRfE2kcVWj+pcKuZtL6Z0Z/ZauhLtMoUl5/CExzyDCK0y1SOBoeWCZJ h0PIMVEBbPBnNagGPOsw8cu13S4/8fZCIdmsOGunO/jEMqNu1Xtlss/Nxh7B58QfrhCw sJjZISbl81hGAzyJ53a4PzZFUjeawJlq1l/pDU2qMtrr96bZ45Kc7mwTfB4/vdwH6BEQ ZhRJsxVjkUul/feu2R6exxlN0W+mMLMTDOh+kizs4Z4QD1n748nn7MDlThbNDQbV+4lj znxg== X-Forwarded-Encrypted: i=1; AJvYcCXCPShCp1X2M9F+Hz9KoKmOI8GTDWj1uGrzXmx99SOf9jfA8r4YqQE59U1XZI4PDqi+Nc8=@vger.kernel.org X-Gm-Message-State: AOJu0YxwSSSqCnkdymHUvtSnd3rN/nxZCCnASYKVwZ1H8EBfQw/YOUMg Prqmvat4aGPT6zQ2RDdYUlrDrn9T8KFOk55lGx77rzyRqicafJOfBKzN7bp7VH5TDyxybqyxyfW 4tltqQQ== X-Received: from oaccj12.prod.google.com ([2002:a05:687c:40c:b0:415:6b50:b04f]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6808:3998:b0:45f:1387:973b with SMTP id 5614622812f47-464bec21345mr6172917b6e.6.1772497616259; Mon, 02 Mar 2026 16:26:56 -0800 (PST) Date: Mon, 2 Mar 2026 16:26:54 -0800 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260227213849.3653331-1-jmattson@google.com> Message-ID: Subject: Re: [kvm-unit-tests PATCH] x86: nVMX: Add retry loop to advanced RTM debugging subtest From: Sean Christopherson To: Yosry Ahmed Cc: Jim Mattson , kvm@vger.kernel.org, Paolo Bonzini Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Mon, Mar 02, 2026, Yosry Ahmed wrote: > On Mon, Mar 2, 2026 at 4:08=E2=80=AFPM Jim Mattson = wrote: > > > IIUC this will be in the order of 100s of milliseconds. Do we need to > > > wait that long between retries? If the CPU is in a state where it wil= l > > > always abort RTM, 30 retries will end up taking seconds or 10s of > > > seconds, right? > > > > I tried reducing the delay by a factor of 10. At 200 retries, I still > > see a 2% skip rate on a Skylake Xeon E5 @ 2GHz. I'd like to get the > > skip rate under 1%. But, maybe others don't care as much? > > > > Yes, 30 billion cycles is going to be on the order of 10 seconds. >=20 > I personally care more about the test time than the fact that it won't > test RTM 2% of the time, but my opinion doesn't really matter :P I generally care more about runtime too, but isn't 10 seconds only the wors= t case scenario, and only on these fubar CPUs? E.g. if there's no perf activ= ity in the host, or the CPU isn't one of these oddballs, isn't XBEGIN going to = succeed ~100% of the time? If this were a choice between "eat N seconds every time" and "skip the test= ", I'd be a-ok with a skip rate of 50% if it meant reducing N. But, assuming = this requires perf activity and a Skylake-era CPU, odds are good this will only = be hit in CI environments, at which point adding ~10 seconds to the worst case sce= nario isn't a bad tradeoff (so long as it doesn't push the total runtime close to= the timeout).