3 ms·
seriously? Mill is/will do speculation before perms? And here I thought turfs were the elegant answer to this nightmare.
by hduty 9y ago
seriously? Mill is/will do speculation before perms? And here I thought turfs were the elegant answer to this nightmare.
- cwzwarich 9y agoSee slide 72 of the metadata talk[1] and slide 51 of the IPC talk[2], which indicate that it does speculation before permissions checking. Since turf permissions operate on the granularity of an arbitrary address range (rather than a page like traditional MMUs), the permissions cache (what the Mill calls a PLB) has a worse latency/power tradeoff than a traditional TLB. The Mill takes advantage of its single address space and reduces some of this hit by doing permissions checks in parallel with the access. [1] https://millcomputing.com/docs/metadata/ https://millcomputing.com/docs/metadata/ [2] https://millcomputing.com/docs/inter-process-communication/ https://millcomputing.com/docs/inter-process-communication/
- willvarfar 9y agoThank you for watching the talks! :D Luckily its not quite as you interpreted: The L1$D is accessed in parallel with the PLB. Both at top-level caches - one for data, one for protection. If there is a PLB miss we have no cache-visible side-effects until the protection has been resolved. The paper we're preparing will cover this in detail, because as you can see, the talks are a bit light on exactly what happens in what order when here.