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Tue, 19 Mar 2024 08:54:45 -0700 (PDT) Message-ID: <094ace88-eea9-4527-b166-9cd83214928d@suse.com> Date: Tue, 19 Mar 2024 16:54:44 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 12/14] xen/arm: add Xen cache colors command line parameter Content-Language: en-US To: Carlo Nonato Cc: Luca Miccio , Andrew Cooper , George Dunlap , Julien Grall , Stefano Stabellini , Wei Liu , Marco Solieri , xen-devel@lists.xenproject.org References: <20240315105902.160047-1-carlo.nonato@minervasys.tech> <20240315105902.160047-13-carlo.nonato@minervasys.tech> 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: <20240315105902.160047-13-carlo.nonato@minervasys.tech> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 15.03.2024 11:59, Carlo Nonato wrote: > From: Luca Miccio > > Add a new command line parameter to configure Xen cache colors. > These colors can be dumped with the cache coloring info debug-key. > > By default, Xen uses the first color. > Benchmarking the VM interrupt response time provides an estimation of > LLC usage by Xen's most latency-critical runtime task. Results on Arm > Cortex-A53 on Xilinx Zynq UltraScale+ XCZU9EG show that one color, which > reserves 64 KiB of L2, is enough to attain best responsiveness: > - Xen 1 color latency: 3.1 us > - Xen 2 color latency: 3.1 us > > More colors are instead very likely to be needed on processors whose L1 > cache is physically-indexed and physically-tagged, such as Cortex-A57. > In such cases, coloring applies to L1 also, and there typically are two > distinct L1-colors. Therefore, reserving only one color for Xen would > senselessly partitions a cache memory that is already private, i.e. > underutilize it. Here you say that using just a single color is undesirable on such systems. > The default amount of Xen colors is thus set to one. Yet then, without any further explanation you conclude that 1 is the universal default. > @@ -147,6 +159,21 @@ void __init llc_coloring_init(void) > panic("Number of LLC colors (%u) not in range [2, %u]\n", > max_nr_colors, CONFIG_NR_LLC_COLORS); > > + if ( !xen_num_colors ) > + { > + unsigned int i; > + > + xen_num_colors = MIN(XEN_DEFAULT_NUM_COLORS, max_nr_colors); > + > + printk(XENLOG_WARNING > + "Xen LLC color config not found. Using first %u colors\n", > + xen_num_colors); > + for ( i = 0; i < xen_num_colors; i++ ) > + xen_colors[i] = i; > + } > + else if ( !check_colors(xen_colors, xen_num_colors) ) > + panic("Bad LLC color config for Xen\n"); This "else" branch again lacks a bounds check against max_nr_colors, if I'm not mistaken. Jan