It is no secret that Intel is getting ready its 14th Technology Meteor Lake to rival the greatest CPUs. The chipmaker has already shared some characteristic units for the upcoming Foveros-packaged chips. Nevertheless, a brand new Linux patch implies that Meteor Lake will sport an L4 cache, which is occasionally used on processors.
The outline from the Linux patch reads: “On MTL, GT can not allocate on LLC – solely the CPU can. This, together with addition of assist for ADM/L4 cache calls a MOCS/PAT desk replace.”
The patch did not specify what “ADM” stands for. It might simply be a flowery advertising title for the L4 cache. The code did not expose the scale of the ADM, both. Traditionally, Intel has used 64MB or 128MB for the eDRAM for Haswell by Espresso Lake. Throughout its Scorching Chips 34 presentation, Intel shared the schematics of the Meteor Lake chip, which contains 4 completely different tiles: CPU tile, SoC tile, IO extender tile, and graphics tile. The quartet sits atop a big base tile that acts as an interposer.
Intel’s first implementation of the eDRAM (embedded DRAM) was with Haswell and served as an L4 cache for the CPU and iGPU. The chipmaker would proceed this follow till Espresso Lake. Nevertheless, just a few chosen desktop and cellular chips leveraged eDRAM over its brief utilization span. Broadwell was essentially the most distinguished structure to characteristic eDRAM. Chipmakers sometimes shun the L4 cache from their designs as a result of it is slower.
The cache hierarchy spans from L1 to L4, however most processors cease at L3 as a result of velocity decreases as you go down the ranks. Decrease-level caches are bigger and thus growing the possibilities of a cache hit. The primary downside is that accessing the decrease caches, resembling L3 and even L4 takes longer. So exterior of feeding the built-in graphics, there are only a few situations the place the L4 cache helps in system efficiency. Nevertheless, in accordance with some Linux patches that Coelacanth’s Dream has unearthed, the L4 cache might make a comeback with Meteor Lake.
The large query is the place Intel will place the ADM/L4 cache. It is potential that Meteor Lake’s base tile could home the L4 cache. For instance, Ponte Vecchio’s base tile carries 144MB of L2 cache, so there’s precedent for it. Alternatively, the L4 cache could reside contained in the SoC tile and will surely clarify its giant panorama.
One other thrilling discovery is that Intel has seemingly blocked Meteor Lake’s iGPU from accessing the LLC (final degree cache). As per the developer notes from the Linux patch (opens in new tab), “On MTL, GT is not allotted on LLC, set has_llc=0.”
LLC corresponds to the highest-numbered cache on the processor the place it has to hit the reminiscence. The L3 is often the LLC in most fashionable processors, shared among the many CPU cores and iGPU. For instance, Intel’s current thirteenth Technology Raptor Lake chips arrive with as much as 36MB of L3 cache, representing a 20% enchancment during the last twelfth Technology Alder Lake components. Nevertheless, the Linux patch states that solely the CPU cores on Meteor Lake can faucet into the LLC. The design is much like AMD’s Ryzen APUs, the place CPU cores and iGPU do not share the identical cache.
A 12-core Meteor Lake processor not too long ago emerged on a benchmark web site. Sadly, the chip’s misreported clock speeds and outcomes could not present a concrete image of how a lot efficiency uplift we are able to count on over Raptor Lake. So it is nonetheless unclear if Meteor Lake will keep cellular solely, like Ice Lake or Tiger Lake, or whether or not it’s going to come to the desktop. Then again, there have been months-long rumors a couple of potential Raptor Lake Refresh, so the latter does not sound unlikely. An alleged Intel doc (opens in new tab) solely confirms that the advertising title for Meteor Lake is 14th Technology Core however does not precisely dispel the rumors.
Meteor Lake ought to hit the retail market within the second half of this yr. After that, the 7nm chips will go up towards some stiff competitors from AMD, together with Dragon Vary (Zen 4 + RDNA 2), Phoenix (Zen 4 + RDNA 3), and the refreshed Rembrandt-R and Barcelo-R chips.