On Tue, Feb 02, 2021 at 10:30:07AM +0200, Avri Altman wrote: > We can make use of this commit, to elaborate some more of the host > control mode logic, explaining what role play each and every variable: > > - activation_thld - In host control mode, reads are the major source of > activation trials. once this threshold hs met, the region is added > to the "to-be-activated" list. Since we reset the read counter upon > write, this include sending a rb command updating the region ppn as > well. > > - normalization_factor - We think of the regions as "buckets". Those > buckets are being filled with reads, and emptied on write. We use > entries_per_srgn - the amount of blocks in a subregion as our bucket > size. This applies because HPB1.0 only concern a single-block > reads. Once the bucket size is crossed, we trigger a normalization > work - not only to avoid overflow, but mainly because we want to > keep those counters normalized, as we are using those reads as a > comparative score, to make various decisions. The normalization is > dividing (shift right) the read counter by the normalization_factor. > If during consecutive normalizations an active region has exhaust > its reads - inactivate it. > > - eviction_thld_enter - Region deactivation is often due to the fact > that eviction took place: a region become active on the expense of > another. This is happening when the max-active-regions limit has > crossed. In host mode, eviction is considered an extreme measure. > We want to verify that the entering region has enough reads, and the > exiting region has much less reads. eviction_thld_enter is the min > reads that a region must have in order to be considered as a > candidate to evict other region. > > - eviction_thld_exit - same as above for the exiting region. A region > is consider to be a candidate to be evicted, only if it has less > reads than eviction_thld_exit. > > - read_timeout_ms - In order not to hang on to “cold” regions, we > shall inactivate a region that has no READ access for a predefined > amount of time - read_timeout_ms. If read_timeout_ms has expired, > and the region is dirty - it is less likely that we can make any > use of HPB-READing it. So we inactivate it. Still, deactivation > has its overhead, and we may still benefit from HPB-READing this > region if it is clean - see read_timeout_expiries. > > - read_timeout_expiries - if the region read timeout has expired, but > the region is clean, just re-wind its timer for another spin. Do > that as long as it is clean and did not exhaust its > read_timeout_expiries threshold. > > - timeout_polling_interval_ms - the frequency in which the delayed > worker that checks the read_timeouts is awaken. You create new sysfs files, but fail to document them in Documentation/ABI/ which is where the above information needs to go :( thanks, greg k-h
