https://github.com/torvalds/linux
Revision a7e69ddb10f72f17556bfe99259ecb10cbcb4b5c authored by Mark on 19 August 2014, 20:45:22 UTC, committed by Greg Kroah-Hartman on 25 August 2014, 17:46:11 UTC
The uSCSI from Newer Technology is a SCSI-USB converter with USB ID 06ca:2003. Like several other SCSI-USB products, it's a Shuttle Technology OEM device. Without a suitable entry in unusual-devs.h, the converter can only access the (single) device with SCSI ID 0. Copying the entry for device 04e6:0002 allows it to work with devices with other SCSI IDs too. There are currently six entries for Shuttle-developed SCSI-USB devices in unusual-devs.h (grep for euscsi): 04e6:0002 Shuttle eUSCSI Bridge USB_SC_DEVICE, USB_PR_DEVICE 04e6:000b Shuttle eUSCSI Bridge USB_SC_SCSI, USB_PR_BULK 04e6:000c Shuttle eUSCSI Bridge USB_SC_SCSI, USB_PR_BULK 050d:0115 Belkin USB SCSI Adaptor USB_SC_SCSI, USB_PR_BULK 07af:0004 Microtech USB-SCSI-DB25 USB_SC_DEVICE, USB_PR_DEVICE 07af:0005 Microtech USB-SCSI-HD50 USB_SC_DEVICE, USB_PR_DEVICE lsusb -v output for the uSCSI lists bInterfaceSubClass 6 SCSI bInterfaceProtocol 80 Bulk (Zip) This patch adds an entry for the uSCSI to unusual_devs.h. Signed-off-by: Mark Knibbs <markk@clara.co.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Tip revision: a7e69ddb10f72f17556bfe99259ecb10cbcb4b5c authored by Mark on 19 August 2014, 20:45:22 UTC
USB: storage: add quirk for Newer Technology uSCSI SCSI-USB converter
USB: storage: add quirk for Newer Technology uSCSI SCSI-USB converter
Tip revision: a7e69dd
split_page_table_lock
Split page table lock
=====================
Originally, mm->page_table_lock spinlock protected all page tables of the
mm_struct. But this approach leads to poor page fault scalability of
multi-threaded applications due high contention on the lock. To improve
scalability, split page table lock was introduced.
With split page table lock we have separate per-table lock to serialize
access to the table. At the moment we use split lock for PTE and PMD
tables. Access to higher level tables protected by mm->page_table_lock.
There are helpers to lock/unlock a table and other accessor functions:
- pte_offset_map_lock()
maps pte and takes PTE table lock, returns pointer to the taken
lock;
- pte_unmap_unlock()
unlocks and unmaps PTE table;
- pte_alloc_map_lock()
allocates PTE table if needed and take the lock, returns pointer
to taken lock or NULL if allocation failed;
- pte_lockptr()
returns pointer to PTE table lock;
- pmd_lock()
takes PMD table lock, returns pointer to taken lock;
- pmd_lockptr()
returns pointer to PMD table lock;
Split page table lock for PTE tables is enabled compile-time if
CONFIG_SPLIT_PTLOCK_CPUS (usually 4) is less or equal to NR_CPUS.
If split lock is disabled, all tables guaded by mm->page_table_lock.
Split page table lock for PMD tables is enabled, if it's enabled for PTE
tables and the architecture supports it (see below).
Hugetlb and split page table lock
---------------------------------
Hugetlb can support several page sizes. We use split lock only for PMD
level, but not for PUD.
Hugetlb-specific helpers:
- huge_pte_lock()
takes pmd split lock for PMD_SIZE page, mm->page_table_lock
otherwise;
- huge_pte_lockptr()
returns pointer to table lock;
Support of split page table lock by an architecture
---------------------------------------------------
There's no need in special enabling of PTE split page table lock:
everything required is done by pgtable_page_ctor() and pgtable_page_dtor(),
which must be called on PTE table allocation / freeing.
Make sure the architecture doesn't use slab allocator for page table
allocation: slab uses page->slab_cache and page->first_page for its pages.
These fields share storage with page->ptl.
PMD split lock only makes sense if you have more than two page table
levels.
PMD split lock enabling requires pgtable_pmd_page_ctor() call on PMD table
allocation and pgtable_pmd_page_dtor() on freeing.
Allocation usually happens in pmd_alloc_one(), freeing in pmd_free() and
pmd_free_tlb(), but make sure you cover all PMD table allocation / freeing
paths: i.e X86_PAE preallocate few PMDs on pgd_alloc().
With everything in place you can set CONFIG_ARCH_ENABLE_SPLIT_PMD_PTLOCK.
NOTE: pgtable_page_ctor() and pgtable_pmd_page_ctor() can fail -- it must
be handled properly.
page->ptl
---------
page->ptl is used to access split page table lock, where 'page' is struct
page of page containing the table. It shares storage with page->private
(and few other fields in union).
To avoid increasing size of struct page and have best performance, we use a
trick:
- if spinlock_t fits into long, we use page->ptr as spinlock, so we
can avoid indirect access and save a cache line.
- if size of spinlock_t is bigger then size of long, we use page->ptl as
pointer to spinlock_t and allocate it dynamically. This allows to use
split lock with enabled DEBUG_SPINLOCK or DEBUG_LOCK_ALLOC, but costs
one more cache line for indirect access;
The spinlock_t allocated in pgtable_page_ctor() for PTE table and in
pgtable_pmd_page_ctor() for PMD table.
Please, never access page->ptl directly -- use appropriate helper.
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