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AJvYcCW5aLTnhRMH0jqNH67+lnULLxcVrWNhFKai40uw05lpkq2pz7dqOMvR74feoNVBVdNpjOo38rwSG2g=@lists.xenproject.org X-Gm-Message-State: AOJu0YysuEU1lNZMX6/bm7kyc8Evg+i1HXJiy2mn5m5ymucpJjUbIIfo k6WFWYeTuZ0t9C4r4pAR2f5I5rUcjR4aXBMyyP2f1Q9NVS8nbm+//Hbr/9OBGg== X-Google-Smtp-Source: AGHT+IE/WHDsBF7A8Nl4XdZMrjrMccybyNAX2IEyxMfeDyg3LK6hqgbgoUYi6QULdLgazAN8FPZiRg== X-Received: by 2002:a17:907:9709:b0:a9a:478:2ee3 with SMTP id a640c23a62f3a-aa4dd71e851mr650827266b.40.1732189148931; Thu, 21 Nov 2024 03:39:08 -0800 (PST) Message-ID: Date: Thu, 21 Nov 2024 12:39:06 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] x86/irq: fix calculation of max PV dom0 pIRQs To: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= Cc: Andrew Cooper , xen-devel@lists.xenproject.org References: <20241120113555.38146-1-roger.pau@citrix.com> <20241120113555.38146-2-roger.pau@citrix.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 21.11.2024 12:04, Roger Pau Monné wrote: > On Thu, Nov 21, 2024 at 11:49:44AM +0100, Jan Beulich wrote: >> On 20.11.2024 12:35, Roger Pau Monne wrote: >>> The current calculation of PV dom0 pIRQs uses: >>> >>> n = min(fls(num_present_cpus()), dom0_max_vcpus()); >>> >>> The usage of fls() is wrong, as num_present_cpus() already returns the number >>> of present CPUs, not the bitmap mask of CPUs. >> >> Hmm. Perhaps that use of fls() should have been accompanied by a comment, but >> I think it might have been put there intentionally, to avoid linear growth. >> Which isn't to say that I mind the adjustment, especially now that we don't >> use any clustered modes anymore for I/O interrupts. I'm merely questioning >> the Fixes: tag, and with that whether / how far to backport. > > Hm, sorry I've assumed the fls() was a typo. It seems wrong to cap > dom0 vCPUs with the fls of the present CPUs number. For consistency, > if the intention was to use fls to limit growth, I would have expected > to also be applied to the dom0 number of vCPUs. FTR: My vague recollection (it has been nearly 10 years) is that I first had it there, too. Until I realized that it hardly ever would have any effect, because of the min(). And for Dom0-s with extremely few vCPU-s it seemed reasonable to not apply that cap there. Jan