| Message ID | 20240412131908.433043-2-ryan.roberts@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Speed up boot with faster linear map creation | expand |
Hi Ryan, On Fri, Apr 12, 2024 at 02:19:06PM +0100, Ryan Roberts wrote: > A large part of the kernel boot time is creating the kernel linear map > page tables. When rodata=full, all memory is mapped by pte. And when > there is lots of physical ram, there are lots of pte tables to populate. > The primary cost associated with this is mapping and unmapping the pte > table memory in the fixmap; at unmap time, the TLB entry must be > invalidated and this is expensive. > > Previously, each pmd and pte table was fixmapped/fixunmapped for each > cont(pte|pmd) block of mappings (16 entries with 4K granule). This means > we ended up issuing 32 TLBIs per (pmd|pte) table during the population > phase. > > Let's fix that, and fixmap/fixunmap each page once per population, for a > saving of 31 TLBIs per (pmd|pte) table. This gives a significant boot > speedup. > > Execution time of map_mem(), which creates the kernel linear map page > tables, was measured on different machines with different RAM configs: > > | Apple M2 VM | Ampere Altra| Ampere Altra| Ampere Altra > | VM, 16G | VM, 64G | VM, 256G | Metal, 512G > ---------------|-------------|-------------|-------------|------------- > | ms (%) | ms (%) | ms (%) | ms (%) > ---------------|-------------|-------------|-------------|------------- > before | 168 (0%) | 2198 (0%) | 8644 (0%) | 17447 (0%) > after | 78 (-53%) | 435 (-80%) | 1723 (-80%) | 3779 (-78%) > > Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> > Tested-by: Itaru Kitayama <itaru.kitayama@fujitsu.com> > Tested-by: Eric Chanudet <echanude@redhat.com> > --- > arch/arm64/mm/mmu.c | 27 ++++++++++++++------------- > 1 file changed, 14 insertions(+), 13 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 495b732d5af3..9f1d69b7b494 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -172,12 +172,9 @@ bool pgattr_change_is_safe(u64 old, u64 new) > return ((old ^ new) & ~mask) == 0; > } > > -static void init_pte(pmd_t *pmdp, unsigned long addr, unsigned long end, > +static void init_pte(pte_t *ptep, unsigned long addr, unsigned long end, > phys_addr_t phys, pgprot_t prot) > { > - pte_t *ptep; > - > - ptep = pte_set_fixmap_offset(pmdp, addr); > do { > pte_t old_pte = __ptep_get(ptep); > > @@ -192,8 +189,6 @@ static void init_pte(pmd_t *pmdp, unsigned long addr, unsigned long end, > > phys += PAGE_SIZE; > } while (ptep++, addr += PAGE_SIZE, addr != end); > - > - pte_clear_fixmap(); > } > > static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr, > @@ -204,6 +199,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr, > { > unsigned long next; > pmd_t pmd = READ_ONCE(*pmdp); > + pte_t *ptep; > > BUG_ON(pmd_sect(pmd)); > if (pmd_none(pmd)) { > @@ -219,6 +215,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr, > } > BUG_ON(pmd_bad(pmd)); > > + ptep = pte_set_fixmap_offset(pmdp, addr); > do { > pgprot_t __prot = prot; > > @@ -229,20 +226,21 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr, > (flags & NO_CONT_MAPPINGS) == 0) > __prot = __pgprot(pgprot_val(prot) | PTE_CONT); > > - init_pte(pmdp, addr, next, phys, __prot); > + init_pte(ptep, addr, next, phys, __prot); > > + ptep += pte_index(next) - pte_index(addr); > phys += next - addr; > } while (addr = next, addr != end); > + > + pte_clear_fixmap(); > } > > -static void init_pmd(pud_t *pudp, unsigned long addr, unsigned long end, > +static void init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end, > phys_addr_t phys, pgprot_t prot, > phys_addr_t (*pgtable_alloc)(int), int flags) > { > unsigned long next; > - pmd_t *pmdp; > > - pmdp = pmd_set_fixmap_offset(pudp, addr); > do { > pmd_t old_pmd = READ_ONCE(*pmdp); > > @@ -268,8 +266,6 @@ static void init_pmd(pud_t *pudp, unsigned long addr, unsigned long end, > } > phys += next - addr; > } while (pmdp++, addr = next, addr != end); > - > - pmd_clear_fixmap(); > } > > static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr, > @@ -279,6 +275,7 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr, > { > unsigned long next; > pud_t pud = READ_ONCE(*pudp); > + pmd_t *pmdp; > > /* > * Check for initial section mappings in the pgd/pud. > @@ -297,6 +294,7 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr, > } > BUG_ON(pud_bad(pud)); > > + pmdp = pmd_set_fixmap_offset(pudp, addr); > do { > pgprot_t __prot = prot; > > @@ -307,10 +305,13 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr, > (flags & NO_CONT_MAPPINGS) == 0) > __prot = __pgprot(pgprot_val(prot) | PTE_CONT); > > - init_pmd(pudp, addr, next, phys, __prot, pgtable_alloc, flags); > + init_pmd(pmdp, addr, next, phys, __prot, pgtable_alloc, flags); > > + pmdp += pmd_index(next) - pmd_index(addr); > phys += next - addr; > } while (addr = next, addr != end); > + > + pmd_clear_fixmap(); > } > > static void alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end, I looked at this specific patch 1/3 for a while and now make sense the code changes to reduce down the number of TLBIs respecting the contigous bit where available at both PMD and PTE levels. I can not finish other 2/3 and 3/3 patches in a timely manner but I'd like to give my Reviewied-by: Itaru Kitayama <itaru.kitayama@fujitsu.com> on 1/3. Thanks, Itaru. > -- > 2.25.1 >
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 495b732d5af3..9f1d69b7b494 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -172,12 +172,9 @@ bool pgattr_change_is_safe(u64 old, u64 new) return ((old ^ new) & ~mask) == 0; } -static void init_pte(pmd_t *pmdp, unsigned long addr, unsigned long end, +static void init_pte(pte_t *ptep, unsigned long addr, unsigned long end, phys_addr_t phys, pgprot_t prot) { - pte_t *ptep; - - ptep = pte_set_fixmap_offset(pmdp, addr); do { pte_t old_pte = __ptep_get(ptep); @@ -192,8 +189,6 @@ static void init_pte(pmd_t *pmdp, unsigned long addr, unsigned long end, phys += PAGE_SIZE; } while (ptep++, addr += PAGE_SIZE, addr != end); - - pte_clear_fixmap(); } static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr, @@ -204,6 +199,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr, { unsigned long next; pmd_t pmd = READ_ONCE(*pmdp); + pte_t *ptep; BUG_ON(pmd_sect(pmd)); if (pmd_none(pmd)) { @@ -219,6 +215,7 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr, } BUG_ON(pmd_bad(pmd)); + ptep = pte_set_fixmap_offset(pmdp, addr); do { pgprot_t __prot = prot; @@ -229,20 +226,21 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr, (flags & NO_CONT_MAPPINGS) == 0) __prot = __pgprot(pgprot_val(prot) | PTE_CONT); - init_pte(pmdp, addr, next, phys, __prot); + init_pte(ptep, addr, next, phys, __prot); + ptep += pte_index(next) - pte_index(addr); phys += next - addr; } while (addr = next, addr != end); + + pte_clear_fixmap(); } -static void init_pmd(pud_t *pudp, unsigned long addr, unsigned long end, +static void init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end, phys_addr_t phys, pgprot_t prot, phys_addr_t (*pgtable_alloc)(int), int flags) { unsigned long next; - pmd_t *pmdp; - pmdp = pmd_set_fixmap_offset(pudp, addr); do { pmd_t old_pmd = READ_ONCE(*pmdp); @@ -268,8 +266,6 @@ static void init_pmd(pud_t *pudp, unsigned long addr, unsigned long end, } phys += next - addr; } while (pmdp++, addr = next, addr != end); - - pmd_clear_fixmap(); } static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr, @@ -279,6 +275,7 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr, { unsigned long next; pud_t pud = READ_ONCE(*pudp); + pmd_t *pmdp; /* * Check for initial section mappings in the pgd/pud. @@ -297,6 +294,7 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr, } BUG_ON(pud_bad(pud)); + pmdp = pmd_set_fixmap_offset(pudp, addr); do { pgprot_t __prot = prot; @@ -307,10 +305,13 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr, (flags & NO_CONT_MAPPINGS) == 0) __prot = __pgprot(pgprot_val(prot) | PTE_CONT); - init_pmd(pudp, addr, next, phys, __prot, pgtable_alloc, flags); + init_pmd(pmdp, addr, next, phys, __prot, pgtable_alloc, flags); + pmdp += pmd_index(next) - pmd_index(addr); phys += next - addr; } while (addr = next, addr != end); + + pmd_clear_fixmap(); } static void alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end,
A large part of the kernel boot time is creating the kernel linear map page tables. When rodata=full, all memory is mapped by pte. And when there is lots of physical ram, there are lots of pte tables to populate. The primary cost associated with this is mapping and unmapping the pte table memory in the fixmap; at unmap time, the TLB entry must be invalidated and this is expensive. Previously, each pmd and pte table was fixmapped/fixunmapped for each cont(pte|pmd) block of mappings (16 entries with 4K granule). This means we ended up issuing 32 TLBIs per (pmd|pte) table during the population phase. Let's fix that, and fixmap/fixunmap each page once per population, for a saving of 31 TLBIs per (pmd|pte) table. This gives a significant boot speedup. Execution time of map_mem(), which creates the kernel linear map page tables, was measured on different machines with different RAM configs: | Apple M2 VM | Ampere Altra| Ampere Altra| Ampere Altra | VM, 16G | VM, 64G | VM, 256G | Metal, 512G ---------------|-------------|-------------|-------------|------------- | ms (%) | ms (%) | ms (%) | ms (%) ---------------|-------------|-------------|-------------|------------- before | 168 (0%) | 2198 (0%) | 8644 (0%) | 17447 (0%) after | 78 (-53%) | 435 (-80%) | 1723 (-80%) | 3779 (-78%) Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> Tested-by: Itaru Kitayama <itaru.kitayama@fujitsu.com> Tested-by: Eric Chanudet <echanude@redhat.com> --- arch/arm64/mm/mmu.c | 27 ++++++++++++++------------- 1 file changed, 14 insertions(+), 13 deletions(-)