Re: Why do flush page cache twice when change TT's cache attribute

[Scott Fang <donnie.fang@xxxxxxxxx>]

Can I do the optimization like:

    if (ttm->caching_state == tt_cached)
 -        drm_clflush_pages(ttm->pages, ttm->num_pages);
+        for (i = 0; i < ttm->num_pages; ++i) 
+           if (PageHighMem(ttm->pages[i]))
+                drm_clflush_pages(&ttm->pages[i], 1);

only do flush cache when high memory and leave the linear memory flush in function set_memory_uc/wc?

2012/3/20 Jerome Glisse <j.glisse@xxxxxxxxx>

On Mon, 2012-03-19 at 23:11 +0800, Scott Fang wrote:
> In function ttm_tt_set_caching
> ,,,,,,,
>
>     if (ttm->caching_state == tt_cached)
>         drm_clflush_pages(ttm->pages, ttm->num_pages);
>
>     for (i = 0; i < ttm->num_pages; ++i) {
>         cur_page = ttm->pages[i];
>         if (likely(cur_page != NULL)) {
>             ret = ttm_tt_set_page_caching(cur_page,
>                               ttm->caching_state,
>                               c_state);
>             if (unlikely(ret != 0))
>                 goto out_err;
>         }
>     }
>
>     ttm->caching_state = c_state;
>
>     return 0;
>
>
> drm_clflush_pages flush cache one time.
> then in the following function
> ttm_tt_set_page_caching->set_memory_wc->change_page_attr_set: in this
> function may flush page cache again.
>
> Does the code do some abundant flush, or there is some trick to these
> codes?
>
> Thanks for the answer in advance.

Yes there might be redundant flushing.

Cheers,
Jerome

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