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Tue, 22 Apr 2025 00:02:11 -0700 (PDT) Message-ID: Date: Tue, 22 Apr 2025 09:02:13 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 10/14] xen/riscv: implementation of aplic and imsic operations To: Oleksii Kurochko Cc: Alistair Francis , Bob Eshleman , Connor Davis , Andrew Cooper , Anthony PERARD , Michal Orzel , Julien Grall , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Stefano Stabellini , Romain Caritey , xen-devel@lists.xenproject.org References: <74a07ed7c596bbcf581010685e01bfdfa19164f5.1744126720.git.oleksii.kurochko@gmail.com> <3426df1b-938a-4d20-a533-dd6695473db0@suse.com> <5f922b70-d4c2-4e6e-ad05-f91afc70ee73@gmail.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: <5f922b70-d4c2-4e6e-ad05-f91afc70ee73@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 18.04.2025 12:43, Oleksii Kurochko wrote: > > On 4/15/25 4:53 PM, Jan Beulich wrote: >> On 08.04.2025 17:57, Oleksii Kurochko wrote: >>> --- a/xen/arch/riscv/imsic.c >>> +++ b/xen/arch/riscv/imsic.c >>> @@ -14,12 +14,68 @@ >>> #include >>> #include >>> #include >>> +#include >>> #include >>> >>> #include >>> >>> static struct imsic_config imsic_cfg; >>> >>> +#define imsic_csr_set(c, v) \ >>> +do { \ >>> + csr_write(CSR_SISELECT, c); \ >>> + csr_set(CSR_SIREG, v); \ >>> +} while (0) >>> + >>> +#define imsic_csr_clear(c, v) \ >>> +do { \ >>> + csr_write(CSR_SISELECT, c); \ >>> + csr_clear(CSR_SIREG, v); \ >>> +} while (0) >> Coming back to these (the later patch adds one more here): How expensive are >> these CSR writes? IOW would it perhaps make sense to maintain a local cache >> of the last written SISELECT value, to avoid writing the same one again if >> the same windowed register needs accessing twice in a row? > > CSRs belong to the HART, so access to them is very fast. Can you back this by any data? I view CSRs as somewhat similar to x86'es MSRs, and access (writes in particular) to some of them is rather slow. Jan