{"id":532571,"date":"2026-07-04T11:06:08","date_gmt":"2026-07-04T11:06:08","guid":{"rendered":"https:\/\/www.newsbeep.com\/ie\/532571\/"},"modified":"2026-07-04T11:06:08","modified_gmt":"2026-07-04T11:06:08","slug":"linux-7-2-rc2-raising-the-default-risc-v-64-bit-cpu-limit-to-256-cores","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/ie\/532571\/","title":{"rendered":"Linux 7.2-rc2 Raising The Default RISC-V 64-bit CPU Limit To 256 Cores"},"content":{"rendered":"

\"RISC-V\"
\nA post merge-window change that landed in Linux Git overnight ahead of tomorrow’s Linux 7.2-rc2 release is bumping the default limit on the number of supported CPU cores for RISC-V 64-bit. Now by default Linux will support up to 256 cores with RISC-V 64-bit kernel builds.<\/p>\n

Up to now RISC-V 64-bit has maintained a NR_CPUS value of 64 for the number of CPU cores to be supported. But merged to Git for Linux 7.2 that default threshold has been bumped to 256 cores\/threads. The NR_CPUS value in turn impacts the size of various static memory allocations and as that number goes higher does slightly increase kernel memory consumption. Meanwhile over on Linux x86_64, most distribution vendor kernels with MAXSMP enabled see NR_CPUS up at 8192 to deal with today’s high core count AMD and Intel server processors. AArch64 (ARM64) even has 512 for its NR_CPUS value or 2048 for LoongArch<\/a>. <\/p>\n

\"RISC-V<\/p>\n

Raising the NR_CPUS for RISC-V came at the request of SpacemiT. The commit bumping the limit explained:
\n
“SpacemiT has already produced a 80-core RVA23 RISC-V server, and going further back, the dual-socket SG2042-based Sophgo Pisces has 128 cores (although that had some issues achieving mainline support). Therefore, an NR_CPUS of 64 is not enough. <\/p>\n

Raise default NR_CPUS to 256 for 64BIT (when !RISCV_SBI_V01, since very old firmware can’t support more than 64 cores). The number was picked as a power of two that is at least double the known max. I believe this should be the right balance between not wasting too much memory and not having to touch this too often. <\/p>\n

Ubuntu has already been shipping NR_CPUS=512 for riscv64. We have also been testing NR_CPUS=256 internally at ISCAS and found negligible performance impact and no ill effects.”<\/p>\n

The only surprising bit is that it was accepted post-merge-window by Linus Torvalds, granted, it shouldn’t have any real regression risk.<\/p>\n

That NR_CPUS increase was merged to Linux Git as part of this week’s RISC-V fixes<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"A post merge-window change that landed in Linux Git overnight ahead of tomorrow’s Linux 7.2-rc2 release is bumping…\n","protected":false},"author":2,"featured_media":532572,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[7165,61,60,7164,7162,7161,7168,7166,7163,7167,7160,7171,80,7169,7170],"class_list":["post-532571","post","type-post","status-publish","format-standard","has-post-thumbnail","category-technology","tag-desktop-linux","tag-ie","tag-ireland","tag-linux-benchmarking","tag-linux-hardware-benchmarks","tag-linux-hardware-reviews","tag-linux-how-to","tag-linux-performance","tag-linux-server-benchmarks","tag-open-source-graphics","tag-phoronix","tag-phoronix-test-suite","tag-technology","tag-ubuntu-benchmarks","tag-ubuntu-hardware"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts\/532571","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/comments?post=532571"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts\/532571\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/media\/532572"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/media?parent=532571"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/categories?post=532571"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/tags?post=532571"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}