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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH V4] xen/privcmd: improve-performance-of-mapping-of-guest
On Wed, Dec 12, 2012 at 10:09:38PM +0000, Mats Petersson wrote:
> One comment asked for more details on the improvements:
> Using a small test program to map Guest memory into Dom0 (repeatedly
> for "Iterations" mapping the same first "Num Pages")
I missed this in my for 3.8 queue. I will queue it up next
week and send it to Linus after a review..
> Iterations Num Pages Time 3.7rc4 Time With this patch
> 5000 4096 76.107 37.027
> 10000 2048 75.703 37.177
> 20000 1024 75.893 37.247
> So a little better than twice as fast.
>
> Using this patch in migration, using "time" to measure the overall
> time it take to migrate a guest (Debian Squeeze 6.0, 1024MB guest
> memory, one network card, one disk, guest at login prompt):
> Time 3.7rc5 Time With this patch
> 6.697 5.667
> Since migration involves a whole lot of other things, it's only about
> 15% faster - but still a good improvement. Similar measurement with a
> guest that is running code to "dirty" memory shows about 23%
> improvement, as it spends more time copying dirtied memory.
>
> As discussed elsewhere, a good deal more can be had from improving the
> munmap system call, but it is a little tricky to get this in without
> worsening non-PVOPS kernel, so I will have another look at this.
>
> ---
> Update since last posting:
> I have just run some benchmarks of a 16GB guest, and the improvement
> with this patch is around 23-30% for the overall copy time, and 42%
> shorter downtime on a "busy" guest (writing in a loop to about 8GB of
> memory). I think this is definitely worth having.
>
> The V4 patch consists of cosmetic adjustments (spelling mistake in
> comment and reversing condition in an if-statement to avoid having an
> "else" branch, a random empty line added by accident now reverted back
> to previous state). Thanks to Jan Beulich for the comments.
>
> The V3 of the patch contains suggested improvements from:
> David Vrabel - make it two distinct external functions, doc-comments.
> Ian Campbell - use one common function for the main work.
> Jan Beulich - found a bug and pointed out some whitespace problems.
>
>
>
> Signed-off-by: Mats Petersson <mats.petersson@xxxxxxxxxx>
>
> ---
> arch/x86/xen/mmu.c | 132
> +++++++++++++++++++++++++++++++++++++++++++------
> drivers/xen/privcmd.c | 55 +++++++++++++++++----
> include/xen/xen-ops.h | 5 ++
> 3 files changed, 169 insertions(+), 23 deletions(-)
>
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index dcf5f2d..a67774f 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -2477,7 +2477,8 @@ void __init xen_hvm_init_mmu_ops(void)
> #define REMAP_BATCH_SIZE 16
>
> struct remap_data {
> - unsigned long mfn;
> + unsigned long *mfn;
> + bool contiguous;
> pgprot_t prot;
> struct mmu_update *mmu_update;
> };
> @@ -2486,7 +2487,13 @@ static int remap_area_mfn_pte_fn(pte_t *ptep,
> pgtable_t token,
> unsigned long addr, void *data)
> {
> struct remap_data *rmd = data;
> - pte_t pte = pte_mkspecial(pfn_pte(rmd->mfn++, rmd->prot));
> + pte_t pte = pte_mkspecial(pfn_pte(*rmd->mfn, rmd->prot));
> + /* If we have a contigious range, just update the mfn itself,
> + else update pointer to be "next mfn". */
> + if (rmd->contiguous)
> + (*rmd->mfn)++;
> + else
> + rmd->mfn++;
>
> rmd->mmu_update->ptr = virt_to_machine(ptep).maddr;
> rmd->mmu_update->val = pte_val_ma(pte);
> @@ -2495,16 +2502,34 @@ static int remap_area_mfn_pte_fn(pte_t *ptep,
> pgtable_t token,
> return 0;
> }
>
> -int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
> - unsigned long addr,
> - unsigned long mfn, int nr,
> - pgprot_t prot, unsigned domid)
> -{
> +/* do_remap_mfn() - helper function to map foreign pages
> + * @vma: the vma for the pages to be mapped into
> + * @addr: the address at which to map the pages
> + * @mfn: pointer to array of MFNs to map
> + * @nr: the number entries in the MFN array
> + * @err_ptr: pointer to array
> + * @prot: page protection mask
> + * @domid: id of the domain that we are mapping from
> + *
> + * This function takes an array of mfns and maps nr pages from that into
> + * this kernel's memory. The owner of the pages is defined by domid. Where
> the
> + * pages are mapped is determined by addr, and vma is used for "accounting"
> of
> + * the pages.
> + *
> + * Return value is zero for success, negative for failure.
> + *
> + * Note that err_ptr is used to indicate whether *mfn
> + * is a list or a "first mfn of a contiguous range". */
> +static int do_remap_mfn(struct vm_area_struct *vma,
> + unsigned long addr,
> + unsigned long *mfn, int nr,
> + int *err_ptr, pgprot_t prot,
> + unsigned domid)
> +{
> + int err, last_err = 0;
> struct remap_data rmd;
> struct mmu_update mmu_update[REMAP_BATCH_SIZE];
> - int batch;
> unsigned long range;
> - int err = 0;
>
> if (xen_feature(XENFEAT_auto_translated_physmap))
> return -EINVAL;
> @@ -2515,9 +2540,15 @@ int xen_remap_domain_mfn_range(struct vm_area_struct
> *vma,
>
> rmd.mfn = mfn;
> rmd.prot = prot;
> + /* We use the err_ptr to indicate if there we are doing a contigious
> + * mapping or a discontigious mapping. */
> + rmd.contiguous = !err_ptr;
>
> while (nr) {
> - batch = min(REMAP_BATCH_SIZE, nr);
> + int index = 0;
> + int done = 0;
> + int batch = min(REMAP_BATCH_SIZE, nr);
> + int batch_left = batch;
> range = (unsigned long)batch << PAGE_SHIFT;
>
> rmd.mmu_update = mmu_update;
> @@ -2526,19 +2557,92 @@ int xen_remap_domain_mfn_range(struct vm_area_struct
> *vma,
> if (err)
> goto out;
>
> - err = HYPERVISOR_mmu_update(mmu_update, batch, NULL, domid);
> - if (err < 0)
> - goto out;
> + /* We record the error for each page that gives an error, but
> + * continue mapping until the whole set is done */
> + do {
> + err = HYPERVISOR_mmu_update(&mmu_update[index],
> + batch_left, &done, domid);
> + if (err < 0) {
> + if (!err_ptr)
> + goto out;
> + /* increment done so we skip the error item */
> + done++;
> + last_err = err_ptr[index] = err;
> + }
> + batch_left -= done;
> + index += done;
> + } while (batch_left);
>
> nr -= batch;
> addr += range;
> + if (err_ptr)
> + err_ptr += batch;
> }
>
> - err = 0;
> + err = last_err;
> out:
>
> xen_flush_tlb_all();
>
> return err;
> }
> +
> +/* xen_remap_domain_mfn_range() - Used to map foreign pages
> + * @vma: the vma for the pages to be mapped into
> + * @addr: the address at which to map the pages
> + * @mfn: the first MFN to map
> + * @nr: the number of consecutive mfns to map
> + * @prot: page protection mask
> + * @domid: id of the domain that we are mapping from
> + *
> + * This function takes a mfn and maps nr pages on from that into this
> kernel's
> + * memory. The owner of the pages is defined by domid. Where the pages are
> + * mapped is determined by addr, and vma is used for "accounting" of the
> + * pages.
> + *
> + * Return value is zero for success, negative ERRNO value for failure.
> + */
> +int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
> + unsigned long addr,
> + unsigned long mfn, int nr,
> + pgprot_t prot, unsigned domid)
> +{
> + return do_remap_mfn(vma, addr, &mfn, nr, NULL, prot, domid);
> +}
> EXPORT_SYMBOL_GPL(xen_remap_domain_mfn_range);
> +
> +/* xen_remap_domain_mfn_array() - Used to map an array of foreign pages
> + * @vma: the vma for the pages to be mapped into
> + * @addr: the address at which to map the pages
> + * @mfn: pointer to array of MFNs to map
> + * @nr: the number entries in the MFN array
> + * @err_ptr: pointer to array of integers, one per MFN, for an error
> + * value for each page. The err_ptr must not be NULL.
> + * @prot: page protection mask
> + * @domid: id of the domain that we are mapping from
> + *
> + * This function takes an array of mfns and maps nr pages from that into this
> + * kernel's memory. The owner of the pages is defined by domid. Where the
> pages
> + * are mapped is determined by addr, and vma is used for "accounting" of the
> + * pages. The err_ptr array is filled in on any page that is not sucessfully
> + * mapped in.
> + *
> + * Return value is zero for success, negative ERRNO value for failure.
> + * Note that the error value -ENOENT is considered a "retry", so when this
> + * error code is seen, another call should be made with the list of pages
> that
> + * are marked as -ENOENT in the err_ptr array.
> + */
> +int xen_remap_domain_mfn_array(struct vm_area_struct *vma,
> + unsigned long addr,
> + unsigned long *mfn, int nr,
> + int *err_ptr, pgprot_t prot,
> + unsigned domid)
> +{
> + /* We BUG_ON because it's a programmer error to pass a NULL err_ptr,
> + * and the consequences later is quite hard to detect what the actual
> + * cause of "wrong memory was mapped in".
> + */
> + BUG_ON(err_ptr == NULL);
> + return do_remap_mfn(vma, addr, mfn, nr, err_ptr, prot, domid);
> +}
> +EXPORT_SYMBOL_GPL(xen_remap_domain_mfn_array);
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 71f5c45..75f6e86 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -151,6 +151,40 @@ static int traverse_pages(unsigned nelem, size_t size,
> return ret;
> }
>
> +/*
> + * Similar to traverse_pages, but use each page as a "block" of
> + * data to be processed as one unit.
> + */
> +static int traverse_pages_block(unsigned nelem, size_t size,
> + struct list_head *pos,
> + int (*fn)(void *data, int nr, void *state),
> + void *state)
> +{
> + void *pagedata;
> + unsigned pageidx;
> + int ret = 0;
> +
> + BUG_ON(size > PAGE_SIZE);
> +
> + pageidx = PAGE_SIZE;
> +
> + while (nelem) {
> + int nr = (PAGE_SIZE/size);
> + struct page *page;
> + if (nr > nelem)
> + nr = nelem;
> + pos = pos->next;
> + page = list_entry(pos, struct page, lru);
> + pagedata = page_address(page);
> + ret = (*fn)(pagedata, nr, state);
> + if (ret)
> + break;
> + nelem -= nr;
> + }
> +
> + return ret;
> +}
> +
> struct mmap_mfn_state {
> unsigned long va;
> struct vm_area_struct *vma;
> @@ -250,7 +284,7 @@ struct mmap_batch_state {
> * 0 for no errors
> * 1 if at least one error has happened (and no
> * -ENOENT errors have happened)
> - * -ENOENT if at least 1 -ENOENT has happened.
> + * -ENOENT if at least one -ENOENT has happened.
> */
> int global_error;
> /* An array for individual errors */
> @@ -260,17 +294,20 @@ struct mmap_batch_state {
> xen_pfn_t __user *user_mfn;
> };
>
> -static int mmap_batch_fn(void *data, void *state)
> +static int mmap_batch_fn(void *data, int nr, void *state)
> {
> xen_pfn_t *mfnp = data;
> struct mmap_batch_state *st = state;
> int ret;
>
> - ret = xen_remap_domain_mfn_range(st->vma, st->va & PAGE_MASK, *mfnp, 1,
> - st->vma->vm_page_prot, st->domain);
> + BUG_ON(nr < 0);
>
> - /* Store error code for second pass. */
> - *(st->err++) = ret;
> + ret = xen_remap_domain_mfn_array(st->vma,
> + st->va & PAGE_MASK,
> + mfnp, nr,
> + st->err,
> + st->vma->vm_page_prot,
> + st->domain);
>
> /* And see if it affects the global_error. */
> if (ret < 0) {
> @@ -282,7 +319,7 @@ static int mmap_batch_fn(void *data, void *state)
> st->global_error = 1;
> }
> }
> - st->va += PAGE_SIZE;
> + st->va += PAGE_SIZE * nr;
>
> return 0;
> }
> @@ -378,8 +415,8 @@ static long privcmd_ioctl_mmap_batch(void __user *udata,
> int version)
> state.err = err_array;
>
> /* mmap_batch_fn guarantees ret == 0 */
> - BUG_ON(traverse_pages(m.num, sizeof(xen_pfn_t),
> - &pagelist, mmap_batch_fn, &state));
> + BUG_ON(traverse_pages_block(m.num, sizeof(xen_pfn_t),
> + &pagelist, mmap_batch_fn, &state));
>
> up_write(&mm->mmap_sem);
>
> diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
> index 6a198e4..22cad75 100644
> --- a/include/xen/xen-ops.h
> +++ b/include/xen/xen-ops.h
> @@ -29,4 +29,9 @@ int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
> unsigned long mfn, int nr,
> pgprot_t prot, unsigned domid);
>
> +int xen_remap_domain_mfn_array(struct vm_area_struct *vma,
> + unsigned long addr,
> + unsigned long *mfn, int nr,
> + int *err_ptr, pgprot_t prot,
> + unsigned domid);
> #endif /* INCLUDE_XEN_OPS_H */
> --
> 1.7.9.5
>
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